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fast-uri EUVDEUVD-2026-64758

| CVE-2026-75931 HIGH
Interpretation Conflict (CWE-436)
2026-08-24 openjs
7.5
CVSS 3.1 · Vendor: openjs
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Severity by source

Vendor (openjs) PRIMARY
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
vuln.today AI
5.9 MEDIUM

AC:H reflects the required application-pattern precondition (two-step validate-then-resolve with scheme-relative input); all other metrics match the supplied vector.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
4.0 AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (openjs).

CVSS VectorVendor: openjs

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

Lifecycle Timeline

3
Analysis Generated
Aug 24, 2026 - 10:23 vuln.today
Patch available
Aug 24, 2026 - 10:02 EUVD
CVE Published
Aug 24, 2026 - 09:30 cve.org
HIGH 7.5

DescriptionCVE.org

fast-uri is a URI parser for Node.js. It canonicalizes a host to its ASCII form only when the input carries an explicit scheme, so a scheme-relative reference such as a host preceded by two slashes is returned with its host verbatim and no error set. As a result fast-uri's own entry points disagree with each other: parse, resolve, normalize, and equal can yield different hosts for the same input depending only on whether a scheme is written out, and equal can return opposite verdicts for the same pair of hosts. An application that extracts a host with fast-uri to check it against a policy list and then resolves the same reference can make its decision on one host while the destination is another, enabling host confusion and policy bypass. The affected versions are 2.4.2 up to but not including 2.4.5, 3.1.3 up to but not including 3.1.6, and 4.0.1 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which canonicalize the host consistently across the resolve path. Users should upgrade to a patched version.

AnalysisAI

Host confusion in fast-uri, a Node.js URI parser in the Fastify ecosystem, allows policy bypass by exploiting inconsistent host canonicalization between the library's own entry points. When a scheme-relative reference (e.g., //unicode-host.example/path) is passed without an explicit scheme, fast-uri's parse, normalize, and equal functions return the host verbatim, while resolve canonicalizes it to ASCII/Punycode - meaning the same input yields different host values depending on which API is called. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Submit scheme-relative URI with non-ASCII host
Delivery
fast-uri parse returns verbatim (non-canonical) host
Exploit
host string passes policy allowlist check
Execution
fast-uri resolve canonicalizes host to ASCII/Punycode form
Persist
Application dispatches request to unintended host
Impact
Security policy bypassed

Vulnerability AssessmentAI

Exploitation The vulnerability requires two specific conditions to be simultaneously true in the target application. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The NVD-assigned CVSS 3.1 vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N scores 7.5 (High). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker targeting a Node.js application that uses fast-uri for SSRF protection submits a request containing a scheme-relative URI such as //внутренний.corp/admin (an internationalized hostname). The application's allowlist check calls fast-uri's parse, which returns the Cyrillic hostname verbatim and matches a permitted pattern. …
Remediation Vendor-released patches are available: upgrade fast-uri to version 2.4.5, 3.1.6, or 4.1.3 depending on the currently installed major/minor branch. … Detailed patch versions, workarounds, and compensating controls in full report.

Recommended ActionAI

Within 24 hours, identify all internal and third-party applications using fast-uri and assess which rely on URI-based policy validation for security decisions. …

Sign in for detailed remediation steps and compensating controls.

Threat intelligence, references, and detailed analysis are available after sign-in.

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EUVD-2026-64758 vulnerability details – vuln.today

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