Perl: Out-of-bounds Read (CVE-2026-15534)
Published Last modified Sources: Ubuntu, BSI, CVE.org, Msrc Update Guide
What is affected, what to do
Perl versions through 5.45.1 have out-of-bounds heap reads and writes during regular expression matching via an undersized superlinear cache in S_regmatch. The regex engine's superlinear cache holds one bit per subject position for each participating WHILEM node, so the bit count is the subject length plus one times the number of nodes.
Update cPanel/WHM to version 136.0.35.
- Affected
- Perl
lte *..5.45.1
- Perl
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Metrics
5.7
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: Vendor (CNA), CVSS v3
5.7
CVSS v3
Severity Medium on the scale from 0 to 10.
Source: Ubuntu, BSI, CVE.org, Msrc Update Guide
0.2 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 5.6
Show all metrics
- Severity
- Medium
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- 51.53 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- 5.7 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- 5.7
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- 0.2 %
- 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- 5.6
- Low — this CVE sits in the lower 10% of all CVEs scored today.
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
- CISA assessment (SSVC)
- Exploitation: none known · not automatable · Technical impact: partial
- Source: CISA Vulnrichment, as of 12 August 2026
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-125, CWE-190, CWE-787
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- Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
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
Perl versions through 5.45.1 have out-of-bounds heap reads and writes during regular expression matching via an undersized superlinear cache in S_regmatch. The regex engine's superlinear cache holds one bit per subject position for each participating WHILEM node, so the bit count is the subject length plus one times the number of nodes. Nothing checks that product for positive overflow of the signed 32-bit count: a 286331153 byte subject matched against a pattern with 15 participating nodes stores the count as 14, leaving a two byte cache. The cache is then indexed from the real match position and node number, so reads go past the end of the allocation, and on failure CACHEsayNO sets a bit past it. A caller that matches an attacker controlled subject of this size against a pattern of this shape can crash the process or corrupt heap memory.
Source: Ubuntu Security Notices, BSI WID Portal, BSI CSAF, cvelistv5, NVD (NIST), Microsoft Security Update Guide
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| — | perl |
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| cPanel | cPanel/WHM |
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Vendors and products
Affected operating systems
| Linux | ubuntu | perl | noble |
Weakness classes (CWE)
CWE-125Out-of-bounds Read
Base
The product reads data past the end, or before the beginning, of the intended buffer.
Entry at MITRE CWE-125CWE-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-190CWE-787Out-of-bounds Write
Base
The product writes data past the end, or before the beginning, of the intended buffer.
Entry at MITRE CWE-787
References & sources
- github.comPerl/perl5/commit/568e6fd238867bb9e99fa3f47cba3169009239e0.patchPatch
- github.comPerl/perl5/commit/54cf3d44cbbedd17d774e9a37921963e8fd5d0cb.patchPatch
- openwall.comlists/oss-security/2026/08/09/12
- openwall.comlists/oss-security/2026/08/09/13
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
Record modifiedCPANSec
Show 5 original changes
Individual changes of this event as published by NVD Type Action Before After Affected versions (publisher) added —Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/15xxx/CVE-2026-15534.json">CVE-2026-15534</a>Reference added —https://github.com/Perl/perl5/commit/54cf3d44cbbedd17d774e9a37921963e8fd5d0cb.patchReference added —https://github.com/Perl/perl5/commit/568e6fd238867bb9e99fa3f47cba3169009239e0.patchReference removed https://github.com/Perl/perl5/commit/54cf3d44cbbedd17d774e9a37921963e8fd5d0cb.patch—Reference removed https://github.com/Perl/perl5/commit/568e6fd238867bb9e99fa3f47cba3169009239e0.patch—Source identifier: 9b29abf9-4ab0-4765-b253-1875cd9b441e
Record modifiedCVE Program
Show 4 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —http://www.openwall.com/lists/oss-security/2026/08/09/12Reference added —http://www.openwall.com/lists/oss-security/2026/08/09/13Reference removed http://www.openwall.com/lists/oss-security/2026/08/09/12—Reference removed http://www.openwall.com/lists/oss-security/2026/08/09/13—Source identifier: af854a3a-2127-422b-91ae-364da2661108
Record modifiedCVE Program
New references:Show the original change
Individual changes of this event as published by NVD Type Action Before After Reference added —http://www.openwall.com/lists/oss-security/2026/08/09/13Source identifier: af854a3a-2127-422b-91ae-364da2661108
Record modifiedCVE Program
New references:Show the original change
Individual changes of this event as published by NVD Type Action Before After Reference added —http://www.openwall.com/lists/oss-security/2026/08/09/12Source identifier: af854a3a-2127-422b-91ae-364da2661108
ReceivedCPANSec
Weakness type: CWE-125, CWE-787, CWE-190
Description added or changed
Show 7 original changes
Individual changes of this event as published by NVD Type Action Before After Affected versions (publisher) added —perlDescription added —Perl versions through 5.45.1 have out-of-bounds heap reads and writes during regular expression matching via an undersized superlinear cache in S_regmatch. The regex engine's superlinear cache holds one bit per subject position for each participating WHILEM node, so the bit count is the subject length plus one times the number of nodes. Nothing checks that product for positive overflow of the signed 32-bit count: a 286331153 byte subject matched against a pattern with 15 participating nodes stores the count as 14, leaving a two byte cache. The cache is then indexed from the real match position and node number, so reads go past the end of the allocation, and on failure CACHEsayNO sets a bit past it. A caller that matches an attacker controlled subject of this size against a pattern of this shape can crash the process or corrupt heap memory.Weakness type (CWE) added —CWE-125Weakness type (CWE) added —CWE-787Weakness type (CWE) added —CWE-190Reference added —https://github.com/Perl/perl5/commit/54cf3d44cbbedd17d774e9a37921963e8fd5d0cb.patchReference added —https://github.com/Perl/perl5/commit/568e6fd238867bb9e99fa3f47cba3169009239e0.patchSource identifier: 9b29abf9-4ab0-4765-b253-1875cd9b441e
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<a href="https://intel.neosec.eu/en/cve/CVE-2026-15534"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-15534.svg?lang=en" alt="CVE-2026-15534 – NEOSEC Intel" height="20"></a>