Vulnerability in fast-uri (CVE-2026-76172)
Summary
Vulnerability in fast-uri (CVE-2026-76172). Data can be tampered with by attackers. Exploitable via undefined. Mitigation: upgrade to 4.1.3 or later.
Original description
The description as published by the source.
Impact
fast-uri decodes percent-encoded characters in the scheme component with the legacy global unescape() and serializes the result back as raw characters, without re-escaping it or validating it as a scheme. A scheme that decodes to characters outside the RFC 3986 scheme grammar can therefore introduce structure the original input did not contain.
For example, %2f%2fevil.example:/pwn parses with no authority (parse().host is undefined), but resolve() and normalize() return //evil.example:/pwn, which reparses with host evil.example. The %uXXXX form (%u002f%u002fevil.example:/pwn) produces the same result, and a scheme containing %0d%0a reaches the output as a raw CR LF.
Applications that normalize or resolve untrusted URLs before a redirect check, host allowlist, or outbound request decision, especially ones that treat a missing authority as same-origin, can be steered to an attacker-chosen authority, and a normalized URI placed in a response header can carry an injected CR LF.
Patches
Upgrade to fast-uri >= 4.1.3, or >= 3.1.6 in the v3.x release line, or >= 2.4.5 in the v2.x release line.
Workarounds
None. Upgrade to the patched version.
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-2026-76172 has been found in fast-uri.
Attackers can target a specific entry point like undefined over the network to misuse the product.
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-2026-76172" on the vendor's site.
CVE-2026-76172 (fast-uri) — CWE-177 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: undefined / evil.example
Patched: 4.1.3 — apply immediately
Workaround: None.
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-177) exists in fast-uri. Attackers reach the vulnerable code path via undefined without authentication.
Check the vendor advisory for the affected versions of fast-uri. Attack surface: undefined / evil.example.
Severity: High (CVSS 7.5/10). Data can be tampered with by attackers.
Update to 4.1.3.
Workaround: None.
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
None.パッチが適用されるまでの応急処置として、None. 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
References
- ATLASSIAN JSWSERVER-26963
- 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