Robots::Validate versions from 0.4.3 before 0.4.10 for Perl report clients as imposter robots when…

Why it is Yellow

• CVSS 7.3 high
• Remotely exploitable without logging in

References

• https://github.com/robrwo/Robots-Validate/commit/776a1456e6605492b7582ed25d3d5006ef384402.patch
• https://metacpan.org/release/RRWO/Robots-Validate-v0.4.10/changes
• https://metacpan.org/release/RRWO/Robots-Validate-v0.4.11/changes
• http://www.openwall.com/lists/oss-security/2026/10/21/30

Original description

Robots::Validate versions from 0.4.3 before 0.4.10 for Perl report clients as imposter robots when User-Agent matcher state carries over from a previous request. Each Robots::Validate object holds one pure-Perl Aho-Corasick search machine and feeds every User-Agent into it without resetting its state. A User-Agent that ends part-way through a robot name leaves the machine mid-match, so the next User-Agent checked by the same object can complete that name. That client's address is then checked against the robot's DNS rule, which it fails. A remote client can use this to make a site that blocks bad robots block other visitors where the prefix User-Agent string is a suffix of a robot being validated. Note that deployments with Algorithm::AhoCorasick::XS are also affected, since it was unused due to a different bug.