Perl: Integer Overflow or Wraparound (CVE-2026-13221)
Published Last modified Sources: Red Hat, BSI, Ubuntu, SUSE, CVE.org, Msrc Update Guide
What is affected, what to do
A flaw was found in Perl. When the Perl regular expression engine processes patterns with a very large number of alternative fixed strings, an internal data field can overflow.
Update Perl to version 5.40.5-RC1, Perl to version 5.42.3-RC1, Perl to version 5.43.10.
- Affected
- Perl
lt *..5.40.5-RC1 - Perl
lt 5.41.0..5.42.3-RC1 - Perl
lt 5.43.0..5.43.10
- Perl
- Fixed in
- Perl
5.40.5-RC1 - Perl
5.42.3-RC1 - Perl
5.43.10
- Perl
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Metrics
9.1
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
4.0
CVSS v3
Severity Medium on the scale from 0 to 10.
Source: Red Hat, BSI, Ubuntu, SUSE, CVE.org, Msrc Update Guide
0.4 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 36.2
Show all metrics
- Severity
- Critical
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 51.68 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- no public PoC known
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 9.1 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 4.0
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 0.4 %
- Low — model estimates < 1% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 36.2
- High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- —
- Published
CWE
CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.
Read in glossary- CWE-190
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
A flaw was found in Perl. When the Perl regular expression engine processes patterns with a very large number of alternative fixed strings, an internal data field can overflow. This leads to silently incorrect regular expression matches, causing the engine to either match strings it should not (false positives) or fail to match strings it should (false negatives). If these regular expressions are used for security-sensitive operations like access control or data filtering, this flaw could result in incorrect security decisions.
Source: redhat_csaf, BSI CSAF, BSI WID Portal, Ubuntu Security Notices, suse_csaf, NVD (NIST), Microsoft Security Update Guide, cvelistv5
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| — | perl |
|
|
| perl | perl |
|
|
| Open Source | Perl |
|
|
| Oracle | Communications |
|
|
Affected operating systems
| Family | Vendor | Product | Version |
|---|---|---|---|
| Linux | ubuntu | perl | bionic |
| Linux | ubuntu | perl | focal |
| Linux | ubuntu | perl | jammy |
| Linux | ubuntu | perl | trusty |
| Linux | ubuntu | perl | xenial |
Weakness classes (CWE)
CWE-190Integer Overflow or Wraparound
Base
The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
Entry at MITRE CWE-190
References & sources
- github.comPerl/perl5/commit/03f74bbbd3a68350d926ee93d56ee4808c28c4c7.patchPatch
- github.comPerl/perl5/issues/23388Issue tracking
- openwall.comlists/oss-security/2026/07/13/5
Reanalysis & status changes
Chronological NVD audit events for this CVE — reanalyses, CVSS updates, CPE diffs.
CVE Modified9b29abf9-4ab0-4765-b253-1875cd9b441e
- Description:
before Perl versions through 5.43.9 produce silently incorrect regular expression matches when an alternation of more than 65535 fixed string branches is compiled into a trie in Perl_study_chunk. When such branches are combined into a trie, the delta between the first branch and the shared tail is stored in a 16-bit field. A branch count above 65535 overflows the field, and the trie's match decision table is truncated with no warning or error. A pattern of this shape produces false positive matches (matching strings it should not) and false negative matches (failing to match strings it should). When such a pattern gates an access or filtering decision, the result is wrong.after Perl versions before 5.40.5-RC1, from 5.41.0 before 5.42.3-RC1, from 5.43.0 before 5.43.10 produce silently incorrect regular expression matches when an alternation of more than 65535 fixed string branches is compiled into a trie in Perl_study_chunk. When such branches are combined into a trie, the delta between the first branch and the shared tail is stored in a 16-bit field. A branch count above 65535 overflows the field, and the trie's match decision table is truncated with no warning or error. A pattern of this shape produces false positive matches (matching strings it should not) and false negative matches (failing to match strings it should). When such a pattern gates an access or filtering decision, the result is wrong. - Affected: after Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/13xxx/CVE-2026-13221.json">CVE-2026-13221</a>
- Reference: after https://github.com/Perl/perl5/commit/03f74bbbd3a68350d926ee93d56ee4808c28c4c7.patch
- Reference: after https://github.com/Perl/perl5/issues/23388
- Description:
CVE Modifiedaf854a3a-2127-422b-91ae-364da2661108
- Reference: after http://www.openwall.com/lists/oss-security/2026/07/13/5
- Reference:
before http://www.openwall.com/lists/oss-security/2026/07/13/5 - Reference Type:
before http://www.openwall.com/lists/oss-security/2026/07/13/5 Types: Mailing List, Patch, Third Party Advisory
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<a href="https://intel.neosec.eu/en/cve/CVE-2026-13221"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-13221.svg?lang=en" alt="CVE-2026-13221 – NEOSEC Intel" height="20"></a>