CVE-2026-112921VulnerabilityPublished 22 Oct 2026Updated 30 Oct 2026

Robots::Validate versions from 0.4.3 before 0.4.10 for Perl report clients as imposter robots when User-Agent matcher

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Authoritative record:CVE-2026-112921· High 7.3

Not known to be exploited · CVSS 7.3 High : upgrade to 0.4.10 soon.

Data as of 30 Oct 2026, 20:25 UTC

CVSS 3.1 base score

7.3High

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CISA-ADP	CVSS 3.1	7.3

EPSS: 0.2% chance of exploitation in 30 days – higher than 13% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 0.4.10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: Low
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 21 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-wh9j-9gh8-wm87

What to do

Upgrade Robots-Validate (Perl module) to 0.4.10.

Affected software

Product	Affected	Fixed in
Robots-Validate	Affected >=0.4.3 <0.4.10	Fixed in 0.4.10
CPANRobots-Validate`pkg:cpan/Robots-Validate`Other threats	Affected >=0.4.3 <0.4.10	Fixed in 0.4.10

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

If you cannot patch yet, users should consider disabling or replacing Robots::Validate or implementing additional validation logic to avoid false positives caused by User-Agent matcher state carryover.

Description

Robots::Validate versions from 0.4.3 up to but not including 0.4.10 for Perl incorrectly identify legitimate clients as imposter robots due to a User-Agent matcher state carryover issue. This occurs because the internal Aho-Corasick search machine does not reset its state between User-Agent checks, allowing a partial match from one User-Agent to affect the next. This flaw can cause legitimate visitors to be blocked if their User-Agent string overlaps with a robot name suffix. The issue also affects deployments using Algorithm::AhoCorasick::XS due to a separate bug preventing its use.

Impact

This vulnerability can cause denial of service to legitimate users by falsely classifying them as imposter robots and blocking their access. It undermines the accuracy of robot detection mechanisms, potentially disrupting normal site traffic and user experience. The CVSS score of 7.3 (high) reflects the network attack vector, low attack complexity, no privileges required, and impacts on confidentiality, integrity, and availability.

Summary

The vulnerability in Robots::Validate versions >=0.4.3 and <0.4.10 arises from the failure to reset the Aho-Corasick search machine state between User-Agent string evaluations. This leads to a scenario where a User-Agent string ending mid-match leaves the matcher in a partial state, causing the subsequent User-Agent to complete a robot name match incorrectly. Consequently, legitimate clients may be falsely identified as imposter robots and blocked based on DNS rules. The problem extends to setups using Algorithm::AhoCorasick::XS, as it is not utilized due to a separate bug, leaving the vulnerable pure-Perl implementation active.

CWE-488Exposure of Data Element to Wrong Session (opens in a new tab)
Base weakness
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.
Architecture and Design
Protect the application's sessions from information leakage. Make sure that a session's data is not used or visible by other sessions.
Testing
Use a static analysis tool to scan the code for information leakage vulnerabilities (e.g. Singleton Member Field).
Architecture and Design
In a multithreading environment, storing user data in Servlet member fields introduces a data access race condition. Do not use member fields to store information in the Servlet.
Attack patterns
Session Credential Falsification through Prediction (opens in a new tab)
Reusing Session IDs (aka Session Replay) (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 20:21 UTC

WeaknessesCWE-488

Technical details

References

Community reviews

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