Vulnerability in fast-uri (CVE-2026-75931)
Summary
Vulnerability in fast-uri (CVE-2026-75931). Data can be tampered with by attackers. Mitigation: upgrade to 4.1.3 or later.
Original description
The description as published by the source.
Impact
fast-uri canonicalizes a host to its ASCII form only when the input carries an explicit scheme. When resolve() resolves a scheme-relative reference (//host/) against a scheme-bearing base, it still emits the host verbatim even though the effective scheme is known, so re-parsing the resolved URI yields a different host than the one resolve() returned. An application that resolves an untrusted reference with fast-uri and then checks or routes on the resulting host can make a policy decision on one host and reach another. This is an incomplete-fix variant of CVE-2026-13676, whose IDN canonicalization was applied only to the scheme-bearing form.
Patches
Upgrade to fast-uri 2.4.5, 3.1.6, or 4.1.3. resolve() now canonicalizes the host once the effective scheme is known, and fails closed if a raw non-ASCII host cannot be converted.
Workarounds
Resolve scheme-relative references against a base that carries a scheme before performing any host-policy or origin check.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-75931 has been found in fast-uri.
Data can be tampered with by attackers. CVSS score: 7.5/10.
What to do: upgrade fast-uri to 4.1.3 or later.
If unsure, ask your IT team or search "fast-uri CVE-2026-75931" on the vendor's site.
CVE-2026-75931 (fast-uri) — CWE-436 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 4.1.3 — apply immediately
Workaround: Resolve scheme-relative references against a base that carries a scheme before performing any host-policy or origin check.
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-436) exists in fast-uri.
Check the vendor advisory for the affected versions of fast-uri.
Severity: High (CVSS 7.5/10). Data can be tampered with by attackers.
Update to 4.1.3.
Workaround: Resolve scheme-relative references against a base that carries a scheme before performing any host-policy or origin check.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'fast-uri' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'fast-uri' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
fast-uriを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply temporary workaround mitigate
Resolve scheme-relative references against a base that carries a scheme before performing any host-policy or origin check.パッチが適用されるまでの応急処置として、Resolve scheme-relative references against a base that carries a scheme before performing any host-policy or origin check. を実施。回避策の副作用 (機能低下) を確認した上で。
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3Apply patch patch
Upgrade fast-uri to 4.1.3ステージング環境で 4.1.3 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
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4Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-75931 node-ajv
- Ubuntu UBUNTU-CVE-2026-75931 node-ajv
References
- patch cna.openjsf.org
- patch github.com
- web nvd.nist.gov
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com