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Full vulnerability report · 2026
CVE-2026-19487High confidence

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

Unknown · Unknown

5.3MediumCVSS 3.1
Recommended action
Within 7 days

Medium technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.

Mitigation available
Distribution package intelligence

Ubuntu vendor package status

Canonical’s release and source-package findings are shown separately from local repository availability.

1 package state
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Ubuntu releaseSource packageVendor stateFixed versionEvidence
Ubuntu 24.04 LTSnoble · standard archiveperlUnder evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.Not published in this feedCanonical record ↗Source updated 9 Sept 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-19487 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityperl: Perl: Incorrect regular expression matching can lead to wrong access or filtering decisions.
326 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • perl as a component of Red Hat Enterprise Linux 10
  • perl-Attribute-Handlers as a component of Red Hat Enterprise Linux 10
  • perl-AutoLoader as a component of Red Hat Enterprise Linux 10
  • perl-AutoSplit as a component of Red Hat Enterprise Linux 10
  • perl-B as a component of Red Hat Enterprise Linux 10
  • perl-Benchmark as a component of Red Hat Enterprise Linux 10
  • perl-Class-Struct as a component of Red Hat Enterprise Linux 10
  • perl-Config-Extensions as a component of Red Hat Enterprise Linux 10
  • perl-DBM_Filter as a component of Red Hat Enterprise Linux 10
  • perl-Devel-Peek as a component of Red Hat Enterprise Linux 10
  • perl-Devel-SelfStubber as a component of Red Hat Enterprise Linux 10
  • perl-DirHandle as a component of Red Hat Enterprise Linux 10
Summary
A flaw was found in Perl. The regular expression engine may produce incorrect match results due to a stale failure flag in the Aho-Corasick prescan, which causes it to end prematurely. This can lead to the engine missing valid matches or matching on the wrong branch. As a result, applications that use regular expressions for critical functions like access control or data filtering could make erroneous decisions, potentially leading to security bypasses or unintended information disclosure.
Remediation
There is no mitigation available. Applications relying on Perl regular expressions for security-critical decisions (access control, input filtering) should implement defense-in-depth measures and monitor for updates.
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-58110

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

Medium technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.

Mitigation available
01

What, why and how

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.

What

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.

Why

The code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

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.

Why

The code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Reference recorded

CISA Vulnrichment records proof-of-concept exploitation in its SSVC data. BlackTree has not independently executed or validated exploit material.

Likely attack path
a network path → Always-Incorrect Control Flow Implementation → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-670 ↗

CWE-670: Always-Incorrect Control Flow Implementation. The code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.ALowAvailability impact: A successful attack can cause a limited loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-670Public exploit reference
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-W-2026-2847Perl: Schwachstelle ermöglicht Denial of Service

Ein entfernter, anonymer Angreifer kann eine Schwachstelle in Perl ausnutzen, um einen Denial of Service Angriff durchzuführen.

Official advisory
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Mitigation available
Affected
perl as a component of Red Hat Enterprise Linux 10; perl-Attribute-Handlers as a component of Red Hat Enterprise Linux 10; perl-AutoLoader as a component of Red Hat Enterprise Linux 10; perl-AutoSplit as a component of Red Hat Enterprise Linux 10; perl-B as a component of Red Hat Enterprise Linux 10; perl-Benchmark as a component of Red Hat Enterprise Linux 10; perl-Class-Struct as a component of Red Hat Enterprise Linux 10; perl-Config-Extensions as a component of Red Hat Enterprise Linux 10; perl-DBM_Filter as a component of Red Hat Enterprise Linux 10; perl-Devel-Peek as a component of Red Hat Enterprise Linux 10; perl-Devel-SelfStubber as a component of Red Hat Enterprise Linux 10; perl-DirHandle as a component of Red Hat Enterprise Linux 10; perl-Dumpvalue as a component of Red Hat Enterprise Linux 10; perl-DynaLoader as a component of Red Hat Enterprise Linux 10; perl-English as a component of Red Hat Enterprise Linux 10; perl-Errno as a component of Red Hat Enterprise Linux 10; perl-ExtUtils-Constant as a component of Red Hat Enterprise Linux 10; perl-ExtUtils-Embed as a component of Red Hat Enterprise Linux 10; perl-ExtUtils-Miniperl as a component of Red Hat Enterprise Linux 10; perl-Fcntl as a component of Red Hat Enterprise Linux 10; perl-File-Basename as a component of Red Hat Enterprise Linux 10; perl-File-Compare as a component of Red Hat Enterprise Linux 10; perl-File-Copy as a component of Red Hat Enterprise Linux 10; perl-File-DosGlob as a component of Red Hat Enterprise Linux 10; perl-File-Find as a component of Red Hat Enterprise Linux 10; perl-File-stat as a component of Red Hat Enterprise Linux 10; perl-FileCache as a component of Red Hat Enterprise Linux 10; perl-FileHandle as a component of Red Hat Enterprise Linux 10; perl-FindBin as a component of Red Hat Enterprise Linux 10; perl-GDBM_File as a component of Red Hat Enterprise Linux 10; and 296 more
Fixed
No fixed version is explicitly recorded in the structured CVE data.
Action
No verified patch reference is present in the current structured sources. Check the vendor advisory before making a change.
Workaround
There is no mitigation available. Applications relying on Perl regular expressions for security-critical decisions (access control, input filtering) should implement defense-in-depth measures and monitor for updates.
04

Evidence and provenance

Published 13 Aug 2026 · Last source change 13 Aug 2026, 20:12 UTC · CWE-670 · Always-Incorrect Control Flow Implementation

CVE recordCVE.org · 5.2
CVSS sourceCISA ADP
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-58110
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD awaiting enrichment

Missing structured fields: affected product. Missing data is not evidence of low risk; review the primary advisory.

Material change intelligence

What changed after publication

View recent updates →

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
ENISA EUVD · EUVD-2026-58110↗Vendor CSAF · Red Hat Product Security↗CISA Vulnrichment SSVC evidence↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-19487 · cve.blacktree.nl