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Perl CVE-2026-19487

| EUVDEUVD-2026-58110 MEDIUM
Always-Incorrect Control Flow Implementation (CWE-670)
2026-08-13 CPANSec GHSA-cg68-cm33-8vqv
Information Disclosure Red Hat
5.3
CVSS 3.1 · Vendor: CPANSec
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Severity by source

Vendor (CPANSec) PRIMARY
5.3 MEDIUM
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
vuln.today AI
6.5 MEDIUM

Network-reachable with no auth; I:L added because incorrect regex results can directly bypass security filter logic per the description.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N
SUSE
MEDIUM
qualitative
Red Hat
6.5 MEDIUM
qualitative

Primary rating from Vendor (CPANSec).

CVSS VectorVendor: CPANSec

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

Lifecycle Timeline

5
Source Code Evidence Fetched
Aug 13, 2026 - 18:46 vuln.today
Analysis Generated
Aug 13, 2026 - 18:46 vuln.today
CVSS changed
Aug 13, 2026 - 18:22 NVD
5.3 (MEDIUM)
CVE Published
Aug 13, 2026 - 15:51 cve.org
UNKNOWN (no severity yet)
CVE Published
Aug 13, 2026 - 15:51 cve.org
MEDIUM 5.3

DescriptionCVE.org

Perl versions from 5.9.4 before 5.41.9 produce incorrect regular expression match results when a stale failure flag ends the Aho-Corasick prescan early in S_find_byclass.

The prescan walks the subject for positions where the full pattern could match, and the engine tries it from the leftmost one recorded. A failing transition sets the failed flag, and a later successful transition does not clear it, so the prescan reads the stale flag as a failure and stops before it can record a candidate that starts earlier. It takes a subject where one candidate is recorded and a later character then forces a fallback through a fail link that succeeds.

Example:

"ABCDE" =~ m/ABCF|BCDE|C/;

matches C at offset 2, not BCDE

"ABCDE" =~ m/ABCF|BCDE|C(G)/;

no match, BCDE missed

An alternation like this can miss input it should match, or match it on the wrong branch, so an access or filtering decision made from the result can be wrong.

AnalysisAI

Incorrect regex match results in Perl 5.9.4 through 5.41.8 allow remote unauthenticated attackers to bypass security filters or access controls that depend on regex alternation patterns. The Aho-Corasick prescan in S_find_byclass carries a stale failure flag that causes it to terminate before recording an earlier valid match candidate, so an alternation like /ABCF|BCDE|C/ against 'ABCDE' may match the wrong branch or return no match at all. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
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Delivery
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Exploit
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Execution
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Vulnerability AssessmentAI

Exploitation Exploitation requires three conditions to converge: (1) the target system runs Perl 5.9.4 through 5.41.8; (2) the vulnerable code path uses a regex with multiple alternation branches structured such that the Aho-Corasick prescan encounters a failing transition before a later successful one - specifically a subject where one candidate is recorded and a later character forces a fallback through a fail link that succeeds; (3) the result of that regex match is used to make a security-relevant decision such as access control, input filtering, or authentication routing. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The official CVSS 5.3 Medium score with vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L significantly understates integrity risk. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Upgrade to Perl 5.41.9 or later, which contains the one-line fix resetting the 'failed' flag on successful Aho-Corasick transitions. … Detailed patch versions, workarounds, and compensating controls in full report.
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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
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CVE-2026-19487 vulnerability details – vuln.today
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