fast-uri: Interpretation Conflict
CVE-2026-13676 is a high-severity interpretation conflict vulnerability in fast-uri, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 4.0.1, 3.1.3 as the first without the flaw, so updating fast-uri to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.69% chance of exploitation within 30 days, higher than 53% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update fast-uri to 4.0.1 or 3.1.3, whichever matches your release line, or a later version.
- Read the advisory on cna.openjsf.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
Version data comes from the organisation that assigned the CVE; 27 further products are omitted here. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N. Scored by CNA.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.5 | High | CNA |
| CVSS 3.1 | 7.5 | High | CNA |
Official description
fast-uri versions 2.3.1 through 3.1.2 and 4.0.0 fail to canonicalize Unicode (IDN) hostnames for HTTP-family URLs. The IDN conversion path calls a helper that does not exist on the global URL constructor, silently leaving the host in its original Unicode form while normalize() and equal() still return values that differ from a WHATWG-compatible URL parser. Applications that use fast-uri to enforce host-based policy (denylists, loopback filtering, redirect validation, outbound proxy routing) before passing the same URL to Node's URL or fetch can be bypassed when the two implementations resolve the same input to different hosts. Patches: upgrade to fast-uri 3.1.3 for the 3.x line or 4.0.1 for the 4.x line. Workarounds: enforce host policy using the same URL parser used for the actual request, or reject non-ASCII hosts before policy checks.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Interpretation Conflict
Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Third-party and government advisories
- access.redhat.com/security/cve/CVE-2026-13676Third Party Advisory
- bugzilla.redhat.com/show_bug.cgi?id=2494197Third Party Advisory
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-13676.jsonThird Party Advisory
Other references
- access.redhat.com/errata/RHSA-2026:37186
- access.redhat.com/errata/RHSA-2026:37585
- access.redhat.com/errata/RHSA-2026:37628
- access.redhat.com/errata/RHSA-2026:40118
- access.redhat.com/errata/RHSA-2026:40262
- access.redhat.com/errata/RHSA-2026:40765
- access.redhat.com/errata/RHSA-2026:40945
- access.redhat.com/errata/RHSA-2026:41066
- access.redhat.com/errata/RHSA-2026:41928
- access.redhat.com/errata/RHSA-2026:41929
- access.redhat.com/errata/RHSA-2026:42815
- access.redhat.com/errata/RHSA-2026:43038
- access.redhat.com/errata/RHSA-2026:44239
- access.redhat.com/errata/RHSA-2026:44268
- access.redhat.com/errata/RHSA-2026:47728
Other vulnerabilities in fast-uri
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
Recent Interpretation Conflict vulnerabilities
- 7.5 High severity
- 9.8 Critical severity
- 7.5 High severity
- 9.1 Critical severity
- 9.1 Critical severity
- 9.1 Critical severity
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