Nest has a Fastify URL Encoding Middleware Bypass

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.2 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-2293: 0.76% estimated exploitation activity in the next 30 days; percentile 55.44 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact What kind of vulnerability is it? Who is impacted? A NestJS application using @nestjs/platform-fastify can allow bypass of any middleware when Fastify path-normalization options (e.g., ignoreTrailingSlash, ignoreDuplicateSlashes, useSemicolonDelimiter) are enabled. In affected route-scoped middleware setups, variant paths may skip middleware checks while still reaching the protected handler. The bug is a path canonicalization mismatch between middleware matching and route matching in Nest’s Fastify adapter. Nest passes Fastify routerOptions (such as ignoreTrailingSlash, ignoreDuplicateSlashes, useSemicolonDelimiter) to the Fastify router in packages/platform-fastify/adapters/fastify-adapter.ts:253. But middleware execution is decided by a separate regex check over req.originalUrl in packages/platform-fastify/adapters/fastify-adapter.ts:706 and packages/platform-fastify/adapters/fastify-adapter.ts:713. If that regex does not match, Nest does next() and skips the middleware…

Published by the source

2 Mar 2026, 14:34 UTC

Last modified by the source

4 Mar 2026, 15:26 UTC

Source last checked

26 Oct 2026, 12:42 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-r4wm-x892-vjmx

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-r4wm-x892-vjmx

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# Patch Next advisory brief: CVE-2026-2293

Advisory: Nest has a Fastify URL Encoding Middleware Bypass
IDs: CVE-2026-2293, GHSA-r4wm-x892-vjmx
Record: https://patchnext.com/advisories/cve-2026-2293 (revision 3, source checked 26 Oct 2026, 12:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @nestjs/platform-fastify 11.1.14. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @nestjs/platform-fastify: affected <= 11.1.13; fixed in 11.1.14

## Suggested inspection (read-only)
- `npm ls @nestjs/platform-fastify --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @nestjs/platform-fastify.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-r4wm-x892-vjmx (OSV record GHSA-r4wm-x892-vjmx lists affected ranges: npm @nestjs/platform-fastify >=0 <11.1.14 (fixed))
- Verified: https://github.com/advisories/GHSA-r4wm-x892-vjmx (GitHub-reviewed advisory GHSA-r4wm-x892-vjmx lists affected ranges: npm @nestjs/platform-fastify >=0 <=11.1.13)

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