Security Onion file analysis with Strelka and YARA: what it answers for your SOC
A team that sees Suricata alerts for a suspicious download but cannot say which file arrived has a gap in its evidence. Strelka scans files extracted from network traffic in Security Onion, and YARA rules are loaded into Strelka so that a file matching a pattern is flagged for review. The question this answers is narrow: what content moved across the wire, and does it match a rule your team trusts. It does not replace endpoint detection and cannot confirm that a file ran on a host. Those answers come from other sources, so the value depends on how the rule set and the analyst workflow fit together.
You need this capability when not knowing the content of a file carries a high cost. Typical triggers include alerts on web or email traffic from unfamiliar hosts, investigations where a user reports an unexpected attachment or download, and environments with obligations to show that inbound files were inspected. The sensor side matters here. Strelka only sees what the sensor extracts, so confirm in the Security Onion documentation for your version which protocols and file types are covered before assuming coverage. During planning, ask for a known test file to be traced end to end through your own sensor and console.
It can wait when the prerequisites are missing. If most of your sensitive traffic is encrypted and you have no lawful way to inspect it at the point of capture, file scanning will miss much of what matters, and that gap should be resolved first. It can also wait if no one owns YARA hit triage, because a rule that fires into an unmonitored queue adds noise without answering anything. Network alerts and log analysis may already meet your current questions. File analysis can be added later on the same sensors once full packet capture and case workflow are settled.
Security Onion is source-available under the Elastic License 2.0, which is not an OSI-approved open-source license. The ELv2 permits you to use and modify the code within its terms, but you should not assume the freedoms an OSI license grants. Have counsel review the license against your intended use, especially if you plan to offer Security Onion-based monitoring to customers, embed it in a product or resell access. The Security Onion Console Detections interface manages the YARA rules loaded into Strelka, and the airgap ISO carries YARA rules for networks without internet access. Confirm how those rules are updated in your environment.
Before enabling file analysis, settle three decisions. First, decide who owns YARA rule changes and who triages hits, with a written path to case creation. Second, test sensor load on your own traffic, because the published hardware minimums describe a starting point, not a measure of your capacity. Third, set a retention rule for extracted files, since they can contain sensitive data. When you request a quote, ask the provider to separate one-time costs, such as design and initial rule tuning, from recurring costs, such as rule maintenance and analyst time.
Configuration choices for file analysis and YARA rules
This table compares the main choices for where YARA rules come from, where the Strelka component runs in a Distributed design, and whether rules are managed in the Console Detections interface. Read each row against its fit column, then confirm the listed points in the vendor documentation before you settle the design. The main takeaway is that rule source, node placement and management path should be decided together, because they shape the update workflow and what depends on the manager.
| Decision | When it fits | What to confirm |
|---|---|---|
| YARA rules bundled with the ISO | Full installs on networks without internet access, or teams that want a tested baseline at install time | Which YARA rule sets the release ships and how they are loaded into Strelka at install |
| Custom YARA rules written by the team | Known malicious file families, internal tooling or organization-specific file patterns the baseline does not cover | How custom rules are added to Strelka, whether the Console can edit them, and how to test for false positives first |
| YARA updates through the soup tool | Connected deployments, or airgapped sites that move newer ISO media in on a schedule | Whether soup updates overwrite local custom rules, and the steps to keep them in place |
| Strelka in a Distributed design | Production deployments, which the architecture docs recommend as the default design | Which node role runs Strelka and file extraction, and how that role is sized and monitored |
| Strelka on a Standalone node | Labs, evaluations or small sites where one host carries every function | Whether file analysis competes with other services for the 24 GB RAM and 4 cores minimum |
| Dependency on the manager node | Any Distributed design, since the manager coordinates the other roles | Which file analysis steps stop when the manager is down, and whether search nodes buffer or drop data |
| Rules managed in Console Detections | Teams that tune NIDS and Sigma rules in the same interface and want one review path | Whether YARA rules can be edited, suppressed or thresholded in the Console, or only loaded |
| Rules managed outside the Console | Teams that need change control in their own repository and approval records before rules go live | Whether Strelka reloads changed files without a restart, and whether manual edits survive soup updates |
How Strelka and YARA scan files from network traffic
Files move through Security Onion in a fixed sequence: sensors observe network traffic, Strelka analyzes the files that are extracted from that traffic, and YARA rules match patterns in file content. The matches are recorded as results that analysts review in the Security Onion Console. Keep this sequence in mind when you plan, because a YARA rule can only match a file that reached Strelka. If extraction does not capture the files you care about, a large and well-written rule set will still show nothing. Test extraction before you spend effort on rule tuning.
In the Distributed deployment type, the manager node, one or more sensor nodes and one or more search nodes divide these roles. Sensors capture and process traffic, and search nodes store and index the resulting data for the Console. The Security Onion architecture docs note that search nodes depend on the manager: if the manager goes down, search nodes stop indexing because they cannot reach Redis. Receiver nodes can add pipeline redundancy and load balancing. Decide early whether manager availability is acceptable for file results, and whether receiver nodes belong in your design. Confirm in the architecture docs exactly where Strelka runs in your chosen layout, because that placement determines which node failures affect file analysis.
The most important unknown in this topic is extraction. Which file types Security Onion extracts from network traffic, and how you control that extraction, are settings that can change between releases. Security Onion 3.0.0 was released on March 31, 2026, and the latest tagged release on GitHub is 3.3.0, published September 11, 2026. Do not assume behavior from a blog post, a forum thread or an older version. Confirm the extraction options in the Security Onion 3 documentation for the exact version you will run, and record the answer in your design document. If the docs do not answer a question clearly, ask the vendor before you commit to a file-based detection use case.
Before you build on this flow, run a short proof of concept in a lab or on a non-production sensor. Send known test files through the monitored path, confirm that Strelka receives them, and confirm that a test YARA rule produces a visible result in the Console. Then stop the manager in the test environment and observe what happens to indexing and to file results. Size sensors against the documented minimums, which are 4 cores, 12 GB RAM and 2 NICs, and plan for more if you expect heavy file traffic. Write down the results so that your operations team can repeat the test after each upgrade.
Setup sequence for Strelka file analysis on Security Onion
This sequence takes a team from confirming the Security Onion 3 platform requirements to a working Strelka and YARA pipeline that has been tested with known files. Each step ends with a check, so the team knows whether to move on. Steps that need internet access or airgap media are marked.
Confirm the platform version and operating system
The platform owner confirms that Security Onion 3 is the target and that every node will run Oracle Linux 9, the only operating system Security Onion 3 supports. Check the latest tagged release on the GitHub releases page, and read the release notes for the version you choose. If you have a 2.4 installation, confirm the upgrade path: 2.4 on Oracle Linux 9 can move to 3 after full packet capture changes from Stenographer to Suricata, while other distributions need a fresh install. Internet access is needed to reach GitHub and the documentation. Where internet access is blocked, get the release notes and ISO through your approved transfer process. Done when the version and operating system are written into the design record.
Size hardware to the minimum node requirements
The infrastructure team maps each planned node to hardware that meets the minimums for its role. Security Onion supports only x86-64 processors. A standalone node needs at least 4 cores, 24 GB RAM, 200 GB storage and 2 NICs. A manager or search node needs 4 cores and 16 GB RAM, and a sensor needs 4 cores, 12 GB RAM and 2 NICs. These are floors, not capacity plans. Traffic volume, retention and full packet capture disk needs are sized separately, so confirm them against your own network. This step needs no internet access. Done when a hardware sheet lists every node, its role, and its specifications against the minimums, and the infrastructure lead has signed it off.
Choose the deployment type for production
The architect selects one of the four deployment types: Import, Evaluation, Standalone or Distributed. For production, Distributed is the recommended design. It uses a manager node, one or more sensor nodes and one or more search nodes. Document the design decision and the reason for it. Note the dependency in the architecture documentation: if the manager goes down, search nodes stop indexing because they cannot reach Redis. Decide whether receiver nodes are needed for pipeline redundancy and load balancing. This step needs no internet access. Done when the design record names each node, its role, and the deployment type, and the team has accepted the single point of dependency on the manager in writing.
Install the nodes and confirm the Console
The platform engineer installs each node from the Security Onion ISO or from the cloud marketplace image, following the install order in the current documentation. An online install pulls packages and rule updates from the internet. A fully airgapped install is also supported: the ISO carries the packages and the NIDS, YARA and Sigma rules, and later updates arrive on newer ISO media through the soup update tool in airgap mode. Confirm the order and media type before starting. Done when every node reports a successful install, the nodes communicate as the design describes, and you can sign in to the Security Onion Console.
Load and review YARA rules in Detections
The detection engineer loads YARA rules into the Security Onion Console Detections interface, where YARA rules are loaded into Strelka. Review each rule source for origin, license and intent before enabling it. Record who approved each rule and why. The documentation describes modify, suppress and threshold tuning for NIDS rules and custom filters for Sigma rules. Confirm which tuning options apply to YARA rules in your version before planning changes. Internet access may be needed to pull upstream rule updates. In an airgapped deployment, the rules come from the ISO or from update media you transfer. Done when the approved YARA rule list appears in the Detections interface with its source and approver recorded.
Validate with test files in the Console
The security engineer runs a controlled test using files that the team has prepared for the purpose. Send known test files through a monitored network path, or use a lab segment that the sensors can see, and confirm that the files are extracted and scanned. Check the Console for results from Strelka and YARA that match the expected outcome. Keep the test files and results as evidence. If a file is not extracted, investigate the sensor path and the protocol first. Encrypted traffic cannot be inspected for file contents, so test with traffic that is visible to the sensors. Internet access is not required for this step. Done when a test file produces the expected result in the Console and the team has documented the test set, the results and any gaps found.
Tuning YARA rules without flooding analysts
Strelka's YARA matches can add file alerts quickly, so the rule set needs an owner, a review step and a testing habit before analysts depend on it. The cards cover the sequence to follow when changing YARA rules in Security Onion, from reviewing bundled rules to deciding how noise is handled. Check each step against the Security Onion version you run.
Review bundled rules before enabling them
Security Onion ships YARA rules with its ISO and loads them into Strelka through the Detections interface. Before enabling a bundled rule, read its logic, the file types it targets and the stated purpose of its author. Enable a small group in a test environment, observe the matches it produces over a representative period, and record which rules you keep, which stay disabled and why. Keeping this record lets the decision survive staff changes and upgrades.
Write custom rules and test on samples
Start each custom YARA rule from samples you already understand: a file confirmed as malicious, a benign file that resembles it, and ordinary files of the same type. Run the rule against all of them and confirm it matches the malicious sample and stays silent on the rest. Keep the samples, expected results and rule version in source control so any later edit can be retested the same way before it reaches production.
Decide who owns rule changes
Every change to a YARA rule changes what analysts see, so one role should approve additions, edits and disablement. Name the owner of the rule set, the reviewers who test proposed changes, and the people allowed to apply changes on the production manager. Document how an analyst requests a change and how urgent changes are handled during an active incident, so a noisy rule is never edited without review.
Confirm what tuning exists for YARA
Security Onion's documented tuning features, including modify, suppress and threshold actions for NIDS rules and custom filters for Sigma rules, are described for those rule types. Before designing a YARA workflow, check the Detections interface in your installed version for each tuning action on YARA rules. Confirm the answer with Security Onion documentation or support for that release, and record it in your rule governance document.
Use suppression and thresholds where supported
Apply suppression and threshold tuning only to rule types where the Detections interface offers it, and attach a reason and a review date to every suppression. For NIDS rules, use the documented modify, suppress or threshold actions. If the interface does not offer tuning for a noisy YARA rule, plan the fix as a rule edit or a disable decision, handled by the same owner and recorded in the same review trail.
Track noise after each change
After each change, compare how often the rule fires with the baseline from testing, and ask analysts which matches they dismissed. Review the file alerts in Security Onion for repeat dismissals of the same rule. Repeated dismissals point to a rule that needs editing, owner review or disabling, so schedule that review before analysts start ignoring the rule's output.
Storage and deduplication: what to confirm before sizing
File storage and any deduplication of repeated files depend on the Security Onion version and how the platform is configured, so this section gives no sizing figure. Settle the questions below before you buy disk, and answer them for the exact release you plan to install. Security Onion 2.4 reached end of life on October 1, 2026, so a new build should be checked against the 3.x documentation. Where the documentation is silent, the reliable source is a test deployment on hardware close to what you plan to buy. Ask your vendor or implementation partner to confirm each point in writing so the answers can be carried into the quote scope.
The first question is what is written to disk. For Strelka, confirm whether extracted file bytes are stored, whether only metadata and scan results are kept, or whether both are kept, and which node holds each. Confirm also where YARA match results are written, and whether they land in Elasticsearch indexes that carry their own retention. A Distributed deployment, with sensor nodes extracting and search nodes indexing, may place data differently from a Standalone install, so run the check on the topology you intend to build. Use a set of benign test files that trigger a known YARA rule, then compare disk usage on each node before and after. Rule changes made in the Detections interface affect what is flagged, so confirm whether they also change what is stored.
The second question is how long extracted files are kept. Find out whether retention for extracted files is set separately from the index lifecycle used for logs and alerts, whether it can differ by node role, and what triggers deletion when space runs low. Ask whether a full disk on a sensor stops extraction, stops Suricata full packet capture, or drops data silently. The architecture documentation states that when the manager goes down, search nodes stop indexing because they cannot reach Redis, so confirm how much data a sensor can hold while disconnected and what happens when that buffer fills. These answers determine how much headroom to buy, and they are best tested by filling a test volume to the cleanup threshold the platform uses.
The third question is how repeated files are handled. Confirm whether identical files, identified by hash, are scanned once and stored once, or scanned and stored each time they appear, and whether that behavior is on by default or a setting you must change. Then confirm how extracted files share storage with Suricata full packet capture, which replaced Stenographer in the 3.0.0 release. Ask whether the two draw from the same disk or pool, which is pruned first, and whether a file can still be recovered from capture after its extracted copy has expired. The sibling page on full packet capture covers capture retention in detail, so use this check only to confirm the interaction, and record the outcome in your sizing worksheet before the purchase order is raised.
Security and operational considerations for extracted files
Extracted files can carry live malware, so the analysis workflow needs its own access rules, isolation and maintenance plan. The cards below cover who can reach extracted content, how the Console and manager are protected, how rules and the platform stay current, and which access controls the Pro edition adds.
Restricting analyst access to extracted content
Files pulled from network traffic may be malicious, and the Strelka results and stored copies are evidence. Decide which roles can view Strelka results, download extracted files and read the associated PCAP before deployment, and confirm how the Console limits those actions for each role in your version. Keep the list of people with download rights short and reviewed.
Isolating the analysis workflow
Treat the Strelka scanning path as a place where untrusted content is handled, and plan where it runs relative to production systems. Decide which sensor and search nodes hold extracted files, whether analyst workstations can reach them directly, and how exported samples leave the environment. Confirm the network segmentation you need with your own security team before the first capture is enabled.
Protecting the Console and manager
The Console and manager node are the control points for detections, Strelka rules and search results, so they need the strongest access protection. Restrict administrative access to named accounts, limit which networks can reach the Console, and log administrative changes. Note that the architecture documentation says search nodes stop indexing if the manager goes down, so plan for manager availability as well as access.
Keeping rules and the platform patched
YARA rules loaded into Strelka and the platform itself both change over time, and both affect what gets flagged. Plan how updates arrive: through soup on connected systems, or through airgap media on networks without internet access, where the ISO carries NIDS, YARA and Sigma rules and soup updates from newer media. Record which rule and platform versions were active during each investigation.
Airgap update media handling
On networks without internet access, rule and platform updates arrive on physical or transferred media, which is itself an intake path for malware. Define who prepares update media, how it is verified before import and where it is staged. Confirm with Security Onion documentation that the media you plan to use matches your version and distribution before running soup against it.
Access controls in Security Onion Pro
The Pro edition adds OIDC single sign-on to the Console, which lets you tie analyst access to your existing identity provider and central account lifecycle. The Pro page also lists LUKS data-at-rest encryption and FIPS mode, which may matter for stored extracted files. Confirm which of these your policies require and whether the free edition meets them, since the Pro edition is a paid, term-based license.
Encrypted traffic and other limits to confirm
A passive sensor can only analyze files it can see in clear text. When a session is encrypted with TLS, the sensor sees the handshake and the encrypted payload, so Strelka may receive no file object to scan, even when the transfer carries malware. This page does not assume decryption. If you need visibility into encrypted web downloads or other encrypted file transfers, decryption is a separate architecture decision. It involves TLS termination or inspection points, key handling, privacy review and the legal basis for inspecting that traffic. Settle that decision before you promise coverage for encrypted channels, and record in the design which channels are out of scope for file analysis.
Supported protocols are the first limit to confirm. File extraction depends on which protocols the sensor components can parse in the version you deploy, and coverage can differ between protocols and between releases. Check the current Security Onion documentation for the protocol list that applies to your version. Then build a list of the transfer types that matter to your organization, such as web downloads, file shares or email attachments (illustrative examples). For each one, run a proof-of-concept on your own traffic and confirm that a file object appears in the Strelka results. Record every protocol that produced no files so the gap appears in your risk register.
File size handling is the next limit. Extraction and scanning both have practical ceilings, and you should get in writing what happens to an object that exceeds them. Confirm whether it is skipped, truncated or scanned in part, and whether the skip is logged. Test with samples near and above the limit, because a silent skip can leave a large payload unscanned while the dashboard looks healthy. Size limits also shape storage and CPU load, so the figures you set should match the deduplication and storage choices discussed elsewhere on this page.
Hardware and platform limits are set by the release you choose. Security Onion supports only x86-64 processors, so ARM or other architectures are not an option for the sensor, manager or search roles. Version 3 supports only Oracle Linux 9. The 3.0.0 release, published March 31, 2026, replaced Stenographer with Suricata for full packet capture. A 2.4 installation can move to 3 only on Oracle Linux 9 after that capture change, and other distributions need a fresh install. Confirm the sensor minimums in the current hardware documentation, which lists 4 cores, 12 GB RAM and 2 NICs, and size the file analysis workload on top of them, since those minimums do not account for your traffic volume.
Treat these checks as a single acceptance test before you commit. Deploy a sensor on a segment that carries representative traffic, include encrypted and unencrypted transfers, and use benign test files alongside any known-test samples your team already trusts. Compare what Strelka reports against what actually crossed the wire, and write down each gap, the protocol or file size involved and the decision it changes. Confirm each limit against the current Security Onion documentation for your exact version, because supported protocols and size handling can change between releases. Bring the results into the design review so the limits shape the rule set, the storage plan and the stated coverage.
Questions teams ask before planning file analysis
What drives the effort of a Security Onion file analysis project?
The main drivers are sensor count, traffic volume, rule governance, storage design and airgap status. Each sensor is another node to build, tune and monitor. Higher traffic means more files to extract and scan, so capacity testing takes longer. Rule governance covers who can change YARA rules in the Detections interface, how changes are reviewed and how false positives are handled. Storage design decides how long extracted content and metadata are kept and where they sit. Airgapped sites add offline media and rule update handling, because the ISO carries NIDS, YARA and Sigma rules and updates arrive as newer media. Ask any partner to show these drivers in a written scope before you compare figures.
Can our internal team run Security Onion file analysis without outside help?
Many teams can, if they already run Linux servers, network sensors and Elastic-based tooling. The harder work is sensor placement, tuning YARA rules to reduce noise, and keeping extraction and storage within capacity as traffic grows. Analysts can modify and manage YARA rules loaded into Strelka from the Detections interface, but someone must own that work over time. Check three things: whether you have an engineer for installation and upgrades (version 3.0.0 supports only Oracle Linux 9), whether analysts will maintain rules after handover, and whether you have time for testing before production. A partner can build the system, hand it over, or support it on retainer.
What does Security Onion file analysis require from our team?
Plan for network access, hardware, a test plan and named rule owners. Sensors need a copy of the traffic you want to inspect, so confirm span or tap access and which network segments are in scope. The published minimums are 4 cores, 12 GB RAM and 2 NICs for a sensor, 4 cores and 16 GB RAM for a manager or search node, and 4 cores, 24 GB RAM, 200 GB storage and 2 NICs for a standalone node. Treat these as floors and size for your traffic. Security Onion supports only x86-64 processors. Build a test plan with sample files and expected detections, and name one person to approve YARA rule changes and one to own the sensors.
How long does planning a file analysis deployment take?
Planning time depends on scope, so no single duration fits every environment. The main variables are the number of sensors, the deployment type (Import, Evaluation, Standalone or Distributed), how many rule sources you govern, and how quickly your team can provide access and approvals. Security Onion recommends a Distributed design for production, which adds manager, sensor and search components to plan. Airgapped networks add time for offline media and update testing. Ask for a written scope with deliverables tied to each phase. DeployOpen agrees most engagements as fixed scope, and quotes follow from that written scope.
Does Security Onion Pro change the file analysis plan?
Pro matters when you need features the free edition lacks, such as OIDC single sign-on to the Console, LUKS data-at-rest encryption or FIPS mode. Pro is sold on 1 to 5 year terms, so the term length belongs in the commercial plan alongside the deployment scope. The extraction, YARA rule and storage design stays the same either way, but encryption and access controls affect where extracted files are stored and who can view them. Confirm with your compliance owner which controls apply before you choose an edition. Check Security Onion Solutions' current Pro terms and support details before you sign.
What happens to file analysis if the manager node goes down?
Search nodes stop indexing when they cannot reach Redis on the manager, so new results stop reaching search. This is why the Distributed design is recommended for production, and why receiver nodes add pipeline redundancy and load balancing. Plan manager backups and recovery steps, and test them before go-live. Confirm with the Security Onion architecture documentation for your version what remains queryable during an outage. Decide in advance what analysts do meanwhile, such as reviewing sensor data directly, so an outage does not stall investigations.
Can YARA rules for Strelka work on an airgapped network?
Yes, Security Onion supports full installs on networks without internet access. The ISO carries packages and NIDS, YARA and Sigma rules, and the soup update tool can apply updates from newer ISO media in airgap mode. The practical work is a repeatable media process: how rule updates are downloaded on a connected system, verified, transferred and applied, and who approves each import. Test each rule update in a staging environment first, because a new YARA rule can flag large volumes of files. Keep a record of each rule set version so detections can be traced during audits. Confirm the exact update steps for your version in the airgap documentation.
What should we ask for in a quote for file analysis?
Ask for a written scope that lists sensors, traffic segments, deployment type, storage design, rule governance, airgap needs and deliverables for each phase. Ask which costs are one-time, such as design, build, testing and handover, and which recur, such as rule maintenance, upgrades, support and Pro term licensing. Ask what the partner needs from you: network access, hardware, test samples and named owners. Ask how upgrades will be handled, since Security Onion 2.4 reaches end of life on October 1, 2026. Request the assumptions and exclusions in writing. DeployOpen does not publish a price list, and its quotes follow from the written scope.
How DeployOpen scopes and delivers Strelka file analysis
DeployOpen plans, implements, documents and supports Security Onion in infrastructure you control, including the file analysis path where Strelka scans files extracted from network traffic with YARA rules. The work starts with a written scope that fixes which file types, sensors, rules and storage limits are in play before any configuration changes are made.
How we scope
- Engagements are fixed-scope, with the file extraction targets, protocols and sensors agreed in writing before work starts.
- The written scope names which YARA rule sets are loaded into Strelka and who approves changes to them.
- Scope records the encrypted traffic areas where file extraction cannot see content, so expectations stay accurate.
How we build
- Configure Strelka and YARA on the Security Onion deployment type chosen for your environment, following the architecture docs.
- Tune YARA rules and Detections settings against sample traffic, recording each suppression or threshold change with a reason.
- Test deduplication and storage behavior against the retention you specified, and confirm results appear in the Console.
How we hand over
- Deliver written runbooks covering extraction scope, rule update steps, storage locations and the limits on encrypted traffic.
- Walk your analysts through reviewing Strelka results in the Console and escalating findings to case workflows.
- Provide a record of every configuration, rule and test result so your team can reproduce the setup later.
How we support
- Ongoing support, upgrades and continuous testing are available as retainers after handover.
- Plan upgrades with attention to Security Onion end-of-life dates and the Oracle Linux 9 requirement for version 3.
- Confirm with your team how rule updates and airgap media will reach the environment if no internet access is available.
