Robots::Validate for Perl reports clients as imposter robots
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- Low · Low · Low
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA.
Summary
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 object reuses its pure-Perl Aho-Corasick search machine without resetting it, so a partial match from one User-Agent can complete a robot name in the next. A remote client can use this to make a site that blocks bad robots block other visitors whose User-Agent is a suffix of a robot being validated, related to CWE-488 (Exposure of Data Element to Wrong Session).
Written with Claude Haiku 5.5 from the sources below · 2026-10-30
Description from the CNA
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| — | Robots-Validate | 0.4.3 to before 0.4.10 | 0.4.10 | Patch available | CNA |
- Robots-Validate Vendor— Affected 0.4.3 to before 0.4.10 Fixed in 0.4.10 Patch available CNA
Remediation
Upgrade Robots-Validate to version 0.4.10. Deployments that use Algorithm::AhoCorasick::XS are also affected, so they need the same upgrade.
Written with Claude Haiku 5.5 from the sources below · 2026-10-30
- Fix · CNA Robots-Validate Fixed in 0.4.10
Timeline
- 2026-10-21 Threatist record created from CVE-2026-112921
- 2026-10-22 Alias added: GHSA-wh9j-9gh8-wm87
- 2026-10-30 CVSS score added · CISA ADP
- 2026-10-30 CISA SSVC decision points changed
References
Sources
- CVE-2026-112921 · CVE Program
- CVE-2026-112921 · NVD
- FIRST EPSS
- GHSA-wh9j-9gh8-wm87 · GitHub Advisory Database · CC BY 4.0
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