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.
History

Fri, 30 Oct 2026 18:30:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 7.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L'}

ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Thu, 22 Oct 2026 11:00:00 +0000

Type Values Removed Values Added
First Time appeared Robrwo
Robrwo robots::validate
Vendors & Products Robrwo
Robrwo robots::validate

Thu, 22 Oct 2026 01:30:00 +0000

Type Values Removed Values Added
References

Wed, 21 Oct 2026 22:00:00 +0000

Type Values Removed Values Added
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.
Title 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
Weaknesses CWE-488
References

cve-icon MITRE

Status: PUBLISHED

Assigner: CPANSec

Published: 2026-10-21T21:37:54.278Z

Updated: 2026-10-30T17:25:36.728Z

Reserved: 2026-10-19T21:17:46.149Z

Link: CVE-2026-112921

cve-icon Vulnrichment

Updated: 2026-10-22T00:16:41.831Z

cve-icon NVD

Status : Deferred

Published: 2026-10-21T22:16:48.527

Modified: 2026-10-30T18:17:21.773

Link: CVE-2026-112921

cve-icon Redhat

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