Login CSRF via plantable OAuth cookies
Published Aug 15, 2026 · Updated Aug 15, 2026
Login CSRF in Fastify @fastify/oauth2 7.2.0 through 8.2.0 allows remote attackers to sign victims in to attacker-controlled accounts. The callback accepts state and PKCE verifier values when they match predictable, unprefixed cookies, without binding either value to the initiating browser. Exploitation requires control of cookie writes for the application host, such as through a sibling subdomain, and only signs the victim in to the attacker's account; it does not expose the victim's account, credentials, or tokens.
Summary
What happened
Login CSRF in Fastify @fastify/oauth2 7.2.0 through 8.2.0 allows remote attackers to sign victims in to attacker-controlled accounts. The callback accepts state and PKCE verifier values when they match predictable, unprefixed cookies, without binding either value to the initiating browser. Exploitation requires control of cookie writes for the application host, such as through a sibling subdomain, and only signs the victim in to the attacker's account; it does not expose the victim's account, credentials, or tokens.
The record
- CVE
- CVE-2026-18165
- Published
- Aug 15, 2026
- Updated
- Aug 15, 2026
- Vendor
- Fastify
- Product
- @fastify/oauth2
- Classifications
- CWE-352
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 15, 2026CVE publishedPublication date reported by the CVE source.
- Aug 15, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=7.2.0 <8.3.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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