---
id: CVE-2026-112921
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
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 Robots::Validate object holds one pure-Perl Aho-Corasick search machi…
severity: none
cwe:
  - CWE-488
product: Robots-Validate
affected:
  - Robots-Validate >= 0.4.3 < 0.4.10
published: '2026-10-21'
updated: '2026-10-22'
sourceUpdated: '2026-10-22T00:16:41.831Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-112921'
references:
  - url: >-
      https://github.com/robrwo/Robots-Validate/commit/776a1456e6605492b7582ed25d3d5006ef384402.patch
  - url: 'https://metacpan.org/release/RRWO/Robots-Validate-v0.4.10/changes'
  - url: 'https://metacpan.org/release/RRWO/Robots-Validate-v0.4.11/changes'
tags:
  - cve.org
ingestedAt: '2026-10-21T22:18:33.747Z'
---

## Overview

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.

## Affected

- `Robots-Validate >= 0.4.3 < 0.4.10`

## Remediation

Upgrade to Robots-Validate v0.4.10 or later.

Deployments with Algorithm::AhoCorasick::XS should upgrade to v0.4.11, which fixed a bug with using that version.