# fast-uri vulnerable to host confusion via failed IDN canonicalization

Advisory record · `GHSA-4c8g-83qw-93j6`

- **Identifiers:** `GHSA-4c8g-83qw-93j6` · `CVE-2026-13676`
- **State:** Confirmed
- **Severity:** CVSS 7.5 High
- **Critical:** No
- **Weakness (CWE):** [CWE-436](https://cwe.mitre.org/data/definitions/436.html) · [CWE-551](https://cwe.mitre.org/data/definitions/551.html)
- **Tags:** [CWE-436](https://agentprime.io/advisories/tag/cwe-436.md) · [CWE-551](https://agentprime.io/advisories/tag/cwe-551.md)
- **Published:** 21 Jul 2026
- **Updated:** 11 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 21 Jul 2026, 19:03 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `fast-uri` (npm): affected `>=4.0.0, <4.0.1 || >=3.0.0, <3.1.3 || >=2.3.1, <2.4.2`; fixed in `4.0.1`, `3.1.3`, `2.4.2`

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 7.5 High, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`, from CNA (openjs)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0069, the 53rd percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

This record came from the full history of the GitHub Advisory Database, published 21 Jul 2026. New records show when each source confirmed them.

## Sources

- [GitHub Advisory Database: GHSA-4c8g-83qw-93j6](https://github.com/advisories/GHSA-4c8g-83qw-93j6)
- [OSV: GHSA-4c8g-83qw-93j6](https://osv.dev/vulnerability/GHSA-4c8g-83qw-93j6)
- <https://github.com/fastify/fast-uri/security/advisories/GHSA-4c8g-83qw-93j6>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-13676>
- <https://github.com/fastify/fast-uri/pull/188>
- <https://github.com/fastify/fast-uri/commit/2a6d357a18a68e6d812824379fd3388a1ae50d05>
- <https://github.com/fastify/fast-uri/commit/21ea1f9d70495c931f55dff893a8fa38f4f2e6bd>
- <https://github.com/fastify/fast-uri/commit/01db48010f594b98f7b323be18b393791c66ed1d>
- <https://access.redhat.com/errata/RHSA-2026:63371>
- <https://access.redhat.com/errata/RHSA-2026:61314>
- <https://access.redhat.com/errata/RHSA-2026:60520>
- <https://access.redhat.com/errata/RHSA-2026:60386>
- <https://access.redhat.com/errata/RHSA-2026:59593>
- <https://access.redhat.com/errata/RHSA-2026:57590>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-4c8g-83qw-93j6>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-4c8g-83qw-93j6/>. Everything for agents: <https://agentprime.io/llms.txt>.