CVE-2026-19487Public exploitNetwork attack vector

Incorrect regex matching via stale prescan failure flag

Published Aug 13, 2026 · Updated Aug 13, 2026

Incorrect regular expression matching in Perl 5.9.4 through 5.41.8 allows attackers to cause wrong application decisions via crafted input. In regexec.c, S_find_byclass leaves the failed flag set after a successful Aho-Corasick fallback transition, so its prescan stops before recording an earlier valid candidate. Exposure depends on an application using affected alternations for attacker-influenced data; a missed or wrong branch can invalidate an access or filtering decision.

CVSS severity5.3
Medium
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect regular expression matching in Perl 5.9.4 through 5.41.8 allows attackers to cause wrong application decisions via crafted input. In regexec.c, S_find_byclass leaves the failed flag set after a successful Aho-Corasick fallback transition, so its prescan stops before recording an earlier valid candidate. Exposure depends on an application using affected alternations for attacker-influenced data; a missed or wrong branch can invalidate an access or filtering decision.

The record

CVE
CVE-2026-19487
Published
Aug 13, 2026
Updated
Aug 13, 2026
Vendor
The Perl Foundation
Product
Perl
Classifications
CWE-670
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 13, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=5.9.4 <5.41.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Perl Foundation · Perlversion=5.9.4 <5.41.9

Published CVSS scores

5.3CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-670Always-Incorrect Control Flow Implementation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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