CVE-2026-18165: @fastify/oauth2 vulnerable to Login CSRF via plantable OAuth state cookies
@fastify/oauth2
Vendor fix available · Affected: @fastify/oauth2 · Exploitation: unlikely (under 1%)
Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.
Higher than 3% of scored CVEs
DescriptionCVE.org
@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.
Affected products1
From the CVE record. A product or version that is not listed is unknown, not unaffected.
- @fastify/oauth2 · @fastify/oauth2from 7.2.0 before 8.3.0
On the Atlas
Every published CVE is on the CyberSIXT Atlas, grouped by weakness, vendor and month.
- Exploitation
- Unlikely (under 1%). EPSS under 1%, or no score yet.
- CISA KEV
- Not listed
- Public check
- No public nuclei template
- Weakness
- Cross-Site Request Forgery
- Published
- August 2026
CoverageNo articles yet
No CyberSIXT article names CVE-2026-18165 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.