# CVE-2026-110008: @fastify/oauth2 login CSRF via state cookie not cleared after callback

Source: https://junglewise.ai/threats/cve-2026-110008-fastify-oauth2-is-a-fastify-wrapper-for-oauth2-login-flows-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-19. Updated: 2026-10-19  
License: CC BY 4.0 with a link back

CVE-2026-110008 · Severity: medium · CVSS 4.2 · Published 2026-10-19

@fastify/oauth2 is a Fastify plugin that handles OAuth2 login flows. A flaw in versions 7.2.0 through 8.3.1 allows attackers to learn a state cookie value and reuse it to log victims into attacker-controlled accounts, because the cookie is set at a login route path but only cleared at the root path. An attacker can drive an OAuth flow in a victim's browser to achieve login CSRF without exposing the victim's credentials or tokens.

Vendors: [Fastify](https://junglewise.ai/threats/vendors/fastify).

## Quick answers

**Is CVE-2026-110008 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-110008 being exploited in the wild.

**How severe is CVE-2026-110008?** Medium severity, with a CVSS score of 4.2, published 19 October 2026.

**Which products and versions are affected?** Fastify @Fastify/Oauth2 7.2.0 through 8.3.1.

**Is there a fix for CVE-2026-110008?** Yes: fixed in @fastify/oauth2 8.3.2. Until then: Set cookie: { path: '/' } in the plugin options to ensure set and clear operations use the same path, or enable hostPrefixedCookies: true (which requires HTTPS) to use __Host- prefixed cookie names. Alternatively, use a single-segment startRedirectPath such as /login. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-110008 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-110008?** Check whether you run Fastify @Fastify/Oauth2 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in @fastify/oauth2 8.3.2

Set cookie: { path: '/' } in the plugin options to ensure set and clear operations use the same path, or enable hostPrefixedCookies: true (which requires HTTPS) to use __Host- prefixed cookie names. Alternatively, use a single-segment startRedirectPath such as /login.

## Technical details

The vulnerability arises from path mismatch during cookie lifecycle: when startRedirectPath has two or more segments and no explicit cookie.path is set, the state and code-verifier cookies are created without a Path attribute (defaulting to the login route's path) but cleared with Path=/. This causes the cookies to survive the OAuth callback, violating the documented single-use guarantee. An attacker observing the state value in authorization URLs can replay it to trigger login CSRF. Attack requires network access and user interaction (visiting an attacker-controlled link in the victim's browser).

## Affected products

- Fastify @fastify/oauth2 7.2.0 through 8.3.1

## Timeline

- 2026-10-19: disclosed

## References

- [https://cna.openjsf.org/security-advisories.html](https://cna.openjsf.org/security-advisories.html)
- [https://github.com/fastify/fastify-oauth2/security/advisories/GHSA-7fcr-mwg4-pw9q](https://github.com/fastify/fastify-oauth2/security/advisories/GHSA-7fcr-mwg4-pw9q)