CVE-2026-18165@fastify/oauth2 vulnerable to Login CSRF via plantable OAuth state cookies
Updated under an hour ago ()
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It affects @fastify/oauth2 and 1 other product. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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@fastify/oauth2 is an OAuth 2.0 plugin for Fastify. In versions from 7.2.0 up to but not including 8.3.0, the plugin validates the OAuth state, and with PKCE the code verifier, by comparing the callback query parameter against an unprefixed, predictable cookie, with no server-side binding to the browser that began the flow. Any party able to write a cookie for the application's host, such as a sibling subdomain under the same registrable domain, can plant matching state and verifier cookies and complete an attacker-owned OAuth flow inside a victim's browser, silently signing the victim in to the attacker's account (login CSRF). It does not expose the victim's own account, credentials, or tokens. The issue is fixed in @fastify/oauth2 8.3.0, which adds an opt-in hostPrefixedCookies option. Users should upgrade to 8.3.0 and enable it, or bind state to a server-side session.
- CVSS
- 4.2 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N
- Weakness (CWE)
- CWE-352
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- openjs
- NVD analysis
- Analyzed
- Record last updated
- Aug 17, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
@fastify/oauth2 @fastify/oauth2 fastify_oauth2:fastify_oauth2 (from the name) | from 7.2.0 before 8.3.0; 8.3.0 not affected | CNA record |
fastify fastify/oauth2 fastify:fastify/oauth2 | from 7.2.0 before 8.3.0 | NVD |
References
- https://github.com/fastify/fastify-oauth2/security/advisories/GHSA-p8h8-rj28-m8q9mitigation, vendor-advisory
- https://cna.openjsf.org/security-advisories.htmlvendor-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.