fix(yara): require corroborating webshell markers - #489
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`php_webshell_known` matched the bare substrings "behinder" and "WSO " under `any of them`, so ordinary prose produced a CRITICAL YR2 finding at 0.9 confidence with a remediation telling the reader to remove a webshell. The German words "behindert" and "Behinderung" contain the first string, and the product name "WSO 2 Micro Integrator" contains the second, as reported in #487. Behinder is now identified by its hardcoded AES key, md5("rebeyond") truncated to 16 characters, which its PHP, ASP and JSP shells share and which signature-base [1] uses for the same purpose. The key is written as a YARA hex string so the packaged rule file does not carry the indicator in plaintext, in the spirit of the encoded malware rules. WSO is identified by the helper names oRb introduced in 2.x: `wsoEx(`, `WSO_VERSION` and `wsoSecParam`. I checked a WSO 2.5 source against the old and new rule: the old one hit only the banner and the bare "WSO " string, the new one hits the banner and all three helpers, so no known sample is lost. I preferred narrowing the strings over a `fullword` modifier because a document that names the Behinder family would still have scored CRITICAL, and "WSO 2" would still have matched. Fixes #487 [1]: https://github.com/Neo23x0/signature-base Signed-off-by: Stefano Amorelli <stefano@amorelli.tech>
The benign cases are the two reproductions from #487 plus a document that names the Behinder and WSO families without shipping them. The malicious cases are a Behinder PHP shell, a Behinder JSP shell and a WSO fragment carrying `WSO_VERSION` and `wsoEx(`. All six fail against the previous rule: the prose cases fired and the samples were missed, so the tests guard both directions. The samples are base64-encoded like the existing reverse shell fixture so the indicators do not sit in the repository in plaintext. Signed-off-by: Stefano Amorelli <stefano@amorelli.tech>
Group family-specific indicators so isolated constants and documented keys do not produce critical findings. Prepared by Codex on behalf of Mohit Gupta. Signed-off-by: Mohit Gupta <mohgupta@nvidia.com>
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Summary
This builds on #488 and preserves the original author attribution while tightening the single-marker cases found during validation.
Fixes #487
Validation
make lintmake format-checkmake docker-smokeSubmitted by Codex on behalf of Mohit Gupta.