CVE-2026-76172 — fast-uri vulnerable to host confusion via percent-encoded scheme normalization
fast-uri is a URI parser for Node.js. During parsing it runs a legacy decoding pass over the scheme component and never re-escapes the result, and serialization writes the scheme back out verbatim, unlike the host component which is re-escaped. As a result an input whose scheme carries percent-encoded slashes parses as a scheme with no authority, so the parsed host and error are both undefined, yet resolving or normalizing that same input emits a network-path reference whose authority is attacker-chosen and re-parses to that host. An application that allowlists on the parsed host, or treats a reference with no authority as safe to resolve against its base, gets the opposite of what it checked, giving an off-site redirect, server-side request forgery, or address-policy bypass. The legacy decoder also expands non-standard escape forms, widening the issue past upstream filters, and control characters in the scheme can reach the output as raw carriage return and line feed. The affected versions are 2.3.1 up to but not including 2.4.5, 3.0.0 up to but not including 3.1.6, and 4.0.0 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which reject a scheme that is not valid after decoding. Users should upgrade to a patched version.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.2% (30-day exploitation probability)+2
- Technical severity (high)+6
- Automatable exploitation (SSVC)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Npm Fast-uri: fixed in version 2.4.5 — github.com (GitHub Security Advisories)
- Npm Fast-uri: fixed in version 3.1.6 — github.com (GitHub Security Advisories)
- Npm Fast-uri: fixed in version 4.1.3 — github.com (GitHub Security Advisories)
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Fast-uri Fast-uri, Openjsf Fast-uri, Npm Fast-uri).
- The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
- Apply the fixed version or the patch documented under Remediation.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Fast-uri | Fast-uri | ≥ 2.3.1 and < 2.4.5≥ 3.0.0 and < 3.1.6≥ 4.0.0 and < 4.1.3 | Vulnerable | CVE Program (cve.org) e CISA ADP |
| Openjsf | Fast-uri | ≥ 2.3.1 and < 2.4.5≥ 3.0.0 and < 3.1.6≥ 4.0.0 and < 4.1.3 | Vulnerable | NIST National Vulnerability Database |
| Npm | Fast-uri | ≥ 2.3.1 and < 2.4.5≥ 3.0.0 and < 3.1.6≥ 4.0.0 and < 4.1.3 | Vulnerable | GitHub Security Advisories |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 7.5 | CVSS 3.1 | High | 3.9 | 3.6 | ce714d77-add3-4f53-aff5-83d477b104bb via NIST National Vulnerability Database |
| 7.5 | CVSS 3.1 | High | — | — | GitHub, Inc. via GitHub Security Advisories |
| 7.5 | CVSS 3.1 | High | — | — | openjs via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N (score shown at the top: ce714d77-add3-4f53-aff5-83d477b104bb) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
EPSS over time FIRST
Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.23%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Timeline
What happened to this CVE, newest first.
- 2026
- Fix documented
- Affected products added · npm/fast-uri
- Affected products added · fast-uri/fast-uri
- SSVC assessment updated
- Record published
- CVSS changed · 7.5
- Source status changed · → Analyzed
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× References added · Oct 14, 2026 – Oct 14, 2026
- 1× Official description updated · Oct 14, 2026 – Oct 14, 2026
References
10 on the record
- cna.openjsf.org/security-advisories.html
- github.com/fastify/fast-uri/security/advisories/GHSA-jqff-g426-hqxp
- github.com/fastify/fast-uri/releases/tag/v4.1.3
- nvd.nist.gov/vuln/detail/CVE-2026-76172
- github.com/fastify/fast-uri/commit/37f3417c82994279656854f83ce938acd81c3862
- github.com/fastify/fast-uri/commit/a941e626411f576f8d90883231e57b6c9d0ff98b
- github.com/fastify/fast-uri/releases/tag/v2.4.5
- github.com/advisories/GHSA-jqff-g426-hqxp
- github.com/fastify/fast-uri/releases/tag/v3.1.6
- github.com/fastify/fast-uri/commit/c6a74bfd9d8c6b0df5362b3c7ae88d8021cb1e39
Elsewhere on this site
Related CVEs (same products)
- High CVE-2026-84394 fast-uri accepts a host that contains an unbalanced or misplaced authority bracket… Sep 3, 2026
- High CVE-2026-84292 fast-uri vulnerable to authority injection via an unvalidated port in serialize Sep 2, 2026
- High CVE-2026-75931 fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references Aug 24, 2026
- High CVE-2026-75975 fast-uri vulnerable to server-side request forgery via malformed IPv6 normalization Aug 24, 2026
- High CVE-2026-75899 fast-uri vulnerable to server-side request forgery via repeated hostname percent-decoding Aug 24, 2026
- High CVE-2026-18446 fast-uri vulnerable to host confusion via backslash authority introducer Jul 31, 2026
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-76172 is "fast-uri vulnerable to host confusion via percent-encoded scheme normalization", rated High. It affects Fast-uri (Fast-uri); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 0.23% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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