URI: Improper Validation of Unsafe Equivalence in Input (CVE-2026-19953)
Published Last modified Sources: Red Hat, BSI, SUSE, CVE.org, Msrc Update Guide
What is affected, what to do
A flaw was found in the URI component for Perl. This vulnerability occurs because the `nameprep` function, responsible for encoding hostnames, does not properly normalize Unicode characters.
Update URI to version 5.36.
- Affected
- URI
lt *..5.36
- URI
- Fixed in
- URI
5.36
- URI
Not sure whether and how you are affected? Ask a question about this vulnerability
Metrics
6.5
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: Vendor (CNA), CVSS v3
6.5
CVSS v3
Severity Medium on the scale from 0 to 10.
Source: Red Hat, BSI, SUSE, CVE.org, Msrc Update Guide
0.2 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 13.8
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- 59.11 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- 6.5 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- 6.5
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- 13.8
- Elevated — this CVE ranks above at least 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 · automatable · Technical impact: partial
- Source: CISA Vulnrichment, as of 1 September 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-1289
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
A flaw was found in the URI component for Perl. This vulnerability occurs because the `nameprep` function, responsible for encoding hostnames, does not properly normalize Unicode characters. As a result, a hostname that is not in a standard Unicode form (non-NFC) can be encoded into a non-standard label. This discrepancy can lead to a situation where security checks, such as allow lists or Server-Side Request Forgery (SSRF) filters, may incorrectly process hostnames, potentially allowing an attacker to bypass security restrictions.
Source: redhat_csaf, BSI WID Portal, BSI CSAF, suse_csaf, NVD (NIST), cvelistv5, 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 | ||
|---|---|---|---|
| — | URI |
|
|
| Red Hat | Enterprise Linux |
|
|
Vendors and products
Weakness classes (CWE)
CWE-1289Improper Validation of Unsafe Equivalence in Input
Base
The product receives an input value that is used as a resource identifier or other type of reference, but it does not validate or incorrectly validates that the input is equivalent to a potentially-unsafe value.
Entry at MITRE CWE-1289
References & sources
- github.comlibwww-perl/URI/commit/956619a9e94f86d8d2c529b4e06a3674c54a73e7…Patch
- github.comlibwww-perl/URI/pull/191Issue tracking
- metacpan.orgrelease/OALDERS/URI-5.36/changesRelease notes
- rfc-editor.orgrfc/rfc5891Technical description
- openwall.comlists/oss-security/2026/08/31/14
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 modifiedCISA ADP
CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
CISA assessment (SSVC): exploitation: none known, automatable: yes
Show 2 original changes
Individual changes of this event as published by NVD Type Action Before After CVSS added —AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:NSSVC assessment added —{"id":"CVE-2026-19953","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-09-01T15:16:46.820304Z"}Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0
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/2026/08/31/14Source identifier: af854a3a-2127-422b-91ae-364da2661108
ReceivedCPANSec
Weakness type: CWE-1289
Description added or changed
Show 7 original changes
Individual changes of this event as published by NVD Type Action Before After Description added —URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep. nameprep lowercases each host label but performs no Unicode normalization. IDNA requires a label to be normalized to Form C before it is encoded (RFC 5891), so a label that is not already in NFC is encoded to a different A-label than its normalized form. A label built from the precomposed Devanagari sequence U+0958 U+093E encodes to xn--72b5c without normalization but to xn--11b2fg after NFC normalization, and xn--72b5c does not round-trip back to the original label. Any caller that reads host() from a URI built from untrusted input and uses it for a security decision (an allow or deny list, an SSRF filter, deduplication, a cache key) sees the non-standard label, while a client that fetches the same URL resolves the NFC form, so the check and the fetch can disagree about the host.Weakness type (CWE) added —CWE-1289Affected versions (publisher) added —New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19953.json">CVE-2026-19953</a>Reference added —https://github.com/libwww-perl/URI/commit/956619a9e94f86d8d2c529b4e06a3674c54a73e7.patchReference added —https://github.com/libwww-perl/URI/pull/191Reference added —https://metacpan.org/release/OALDERS/URI-5.36/changesReference added —https://www.rfc-editor.org/rfc/rfc5891#section-5.2Source identifier: 9b29abf9-4ab0-4765-b253-1875cd9b441e
Embed badge
Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.
<a href="https://intel.neosec.eu/en/cve/CVE-2026-19953"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-19953.svg?lang=en" alt="CVE-2026-19953 – NEOSEC Intel" height="20"></a>