CGI: Incorrect Behavior Order: Validate Before Canonicalize (CVE-2026-120638)
Published Last modified Sources: CVE.org
What is affected, what to do
CGI versions before 5.00 for Perl allow open redirects via HTML entity decoding of the URL after application validation in redirect. redirect decodes HTML entities in its URL before writing the Location header, so a URL the application has already validated can change meaning. For example, //evil.example/ becomes //evil.example/ and sends the user to another host.
Update CGI to version 5.00.
- Affected
- CGI
lt *..5.00
- CGI
- Fixed in
- CGI
5.00
- CGI
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Metrics
—
Priority
No value is available for this vulnerability.
—
CVSS v3
No value is available for this vulnerability.
0.2 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 7.7
Show all metrics
- Severity
- Not rated
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- 30.00 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
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- 7.7
- 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
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-180, CWE-601
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
CGI versions before 5.00 for Perl allow open redirects via HTML entity decoding of the URL after application validation in redirect. redirect decodes HTML entities in its URL before writing the Location header, so a URL the application has already validated can change meaning. For example, //evil.example/ becomes //evil.example/ and sends the user to another host.
Source: NVD (NIST), cvelistv5
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| — | CGI |
|
|
Weakness classes (CWE)
CWE-180Incorrect Behavior Order: Validate Before Canonicalize
Variant
The product validates input before it is canonicalized, which prevents the product from detecting data that becomes invalid after the canonicalization step.
Entry at MITRE CWE-180CWE-601URL Redirection to Untrusted Site ('Open Redirect')
Base
The web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a redirect.
Entry at MITRE CWE-601
References & sources
- github.comleejo/CGI.pm/commit/7733c2753f4f240012097507cda2b6e87ae46db4.pa…Patch
- metacpan.orgrelease/LEEJO/CGI-4.72/source/lib/CGI.pmTechnical description
- metacpan.orgrelease/LEEJO/CGI-5.00/changesRelease notes
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).
ReceivedCPANSec
Weakness type: CWE-601, CWE-180
Description added or changed
Show 7 original changes
Individual changes of this event as published by NVD Type Action Before After Description added —CGI versions before 5.00 for Perl allow open redirects via HTML entity decoding of the URL after application validation in redirect. redirect decodes HTML entities in its URL before writing the Location header, so a URL the application has already validated can change meaning. For example, //evil.example/ becomes //evil.example/ and sends the user to another host.Weakness type (CWE) added —CWE-601Weakness type (CWE) added —CWE-180Affected versions (publisher) added —New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/120xxx/CVE-2026-120638.json">CVE-2026-120638</a>Reference added —https://github.com/leejo/CGI.pm/commit/7733c2753f4f240012097507cda2b6e87ae46db4.patchReference added —https://metacpan.org/release/LEEJO/CGI-4.72/source/lib/CGI.pmReference added —https://metacpan.org/release/LEEJO/CGI-5.00/changesSource identifier: 9b29abf9-4ab0-4765-b253-1875cd9b441e
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<a href="https://intel.neosec.eu/en/cve/CVE-2026-120638"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-120638.svg?lang=en" alt="CVE-2026-120638 – NEOSEC Intel" height="20"></a>