# CVE-2026-86472: node-ajv: fast-uri is a dependency-free RFC 3986 URI parser for Node.js, used by Fastify and ajv

CVE-2026-86472 is fixed in 5 products on 1 platform, first by DEBIAN-CVE-2026-86472, released September 20, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-86472
- Priority: Routine
- CVSS: 4.8 (medium)
- EPSS: 0.0025
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 15, 2026

## Description

fast-uri is a dependency-free RFC 3986 URI parser for Node.js, used by Fastify and ajv. In versions before 2.4.7, from 3.0.0 through 3.1.7, and from 4.0.0 through 4.1.4, fast-uri folds the host to lowercase before it percent-decodes the host, so a percent-encoded uppercase octet such as %41 decodes to a literal A that is never folded. For a scheme-relative reference such as //host there is no scheme, so the host canonicalization that would normally repair this does not run, and parse, normalize, and equal then disagree on the same host. An application that makes a case-sensitive host decision on fast-uri output, for example a host allowlist or denylist that compares the parsed host or uses equal, can be steered past the check with a percent-encoded uppercase octet, and because hostnames are case-insensitive in DNS and HTTP the evading spelling still reaches the host the check meant to gate. The issue is fixed in fast-uri 2.4.7, 3.1.8, and 4.1.5, and users should upgrade to one of those versions or later. As a workaround, compare hosts case-insensitively by lowercasing the parsed host before any allowlist or denylist decision.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | node-ajv Debian 14 | 8.20.0~ds+~cs7.1.6-1 | [DEBIAN-CVE-2026-86472](https://patchblox.com/security/data/fix/linux/debian-cve-2026-86472.md) | Sep 20, 2026 |
| Linux | python-jupytext Fedora 43 | 1.19.6-1.fc43 | [FEDORA-2026-3942AB86FD](https://patchblox.com/security/data/fix/linux/fedora-2026-3942ab86fd.md) | Oct 5, 2026 |
| Linux | python-jupytext-doc Fedora 43 | 1.19.6-1.fc43 | [FEDORA-2026-3942AB86FD](https://patchblox.com/security/data/fix/linux/fedora-2026-3942ab86fd.md) | Oct 5, 2026 |
| Linux | python3-jupyterlab-jupytext Fedora 43 | 1.19.6-1.fc43 | [FEDORA-2026-3942AB86FD](https://patchblox.com/security/data/fix/linux/fedora-2026-3942ab86fd.md) | Oct 5, 2026 |
| Linux | python3-jupytext Fedora 43 | 1.19.6-1.fc43 | [FEDORA-2026-3942AB86FD](https://patchblox.com/security/data/fix/linux/fedora-2026-3942ab86fd.md) | Oct 5, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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