CPANSA-Robots-Validate-2026-112921: Robots-Validate vulnerability
| Publisher | giterlizzi | Document category | csaf_security_advisory |
|---|---|---|---|
| Initial release date | 2026-10-21T00:00:00 | Engine | CSAF Perl Toolkit 0.26 |
| Current release date | 2026-10-21T00:00:00 | Build Date | |
| Current version | 1 | Status | final |
| CVSS v3.1 Base Score | Severity | ||
| Original language | Language | en | |
| Also referred to | |||
Vulnerability 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.
Vulnerabilities
CVE-2026-112921
Vulnerability DescriptionRobots::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.
| Weakness | CWE-488 : Exposure of Data Element to Wrong Session |
|---|
Product status
Known affected
| Product | Score | ||||
|---|---|---|---|---|---|
| Robots-Validate greater than 0.4.2 and less than 0.4.10 |
|
Fixed
- Robots-Validate greater than or equal 0.4.10
giterlizzi
Namespace: https://github.com/giterlizzi/
gdt@cpan.org
References
- CPANSA-Robots-Validate-2026-112921 JSON self
https://raw.githubusercontent.com/giterlizzi/perl-CPANSA-CSAF/develop/csaf/white/2026/cpansa-robots-validate-2026-112921.json - https://github.com/robrwo/Robots-Validate/commit/776a1456e6605492b7582ed25d3d5006ef384402.patch external
https://github.com/robrwo/Robots-Validate/commit/776a1456e6605492b7582ed25d3d5006ef384402.patch - https://metacpan.org/release/RRWO/Robots-Validate-v0.4.10/changes external
https://metacpan.org/release/RRWO/Robots-Validate-v0.4.10/changes - https://metacpan.org/release/RRWO/Robots-Validate-v0.4.11/changes external
https://metacpan.org/release/RRWO/Robots-Validate-v0.4.11/changes - http://www.openwall.com/lists/oss-security/2026/10/21/30 external
http://www.openwall.com/lists/oss-security/2026/10/21/30 - CVE-2026-112921 (NVD) external
https://nvd.nist.gov/vuln/detail/CVE-2026-112921
Revision history
| Version | Date of the revision | Summary of the revision |
|---|---|---|
| 1 | Wed Oct 21 00:00:00 2026 | First release |
Sharing rules
TLP:WHITE
For the TLP version see: https://www.first.org/tlp/