CVE-2026-112921
Received
Received - Intake
State Carry-Over in Robots::Validate Allows Imposter Robot Detection Bypass
Vulnerability report for CVE-2026-112921, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-10-21
Last updated on: 2026-10-21
Assigner: CPANSec
Description
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.
CVSS Scores
EPSS Scores
| Probability: | |
| Percentile: |
Meta Information
Affected Vendors & Products
Currently, no data is known.
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-488 | The product does not sufficiently enforce boundaries between the states of different sessions, causing data to be provided to, or used by, the wrong session. |
