CVE-2026-27804: Parse Server: Account takeover via JWT algorithm confusion in Google auth adapter
Impact
An unauthenticated attacker can forge a Google authentication token with alg: "none" to log in as any user linked to a Google account, without knowing their credentials. All deployments with Google authentication enabled are affected.
Patches
The fix hardcodes the expected RS256 algorithm instead of trusting the JWT header, and replaces the Google adapter's custom key fetcher with jwks-rsa which rejects unknown key IDs.
Workarounds
Disable Google authentication until you can upgrade.
References
- GitHub advisory: https://github.com/parse-community/parse-server/security/advisories/GHSA-4q3h-vp4r-prv2 - Fixed in Parse Server 9.3.1-alpha.4: https://github.com/parse-community/parse-server/releases/tag/9.3.1-alpha.4 - Fixed in Parse Server 8.6.3: https://github.com/parse-community/parse-server/releases/tag/8.6.3
Other sources
Parse Server is an open source backend that can be deployed to any infrastructure that can run Node.js. Prior to versions 8.6.3 and 9.1.1-alpha.4, an unauthenticated attacker can forge a Google authentication token with alg: "none" to log in as any user linked to a Google account, without knowing their credentials. All deployments with Google authentication enabled are affected. The fix in versions 8.6.3 and 9.1.1-alpha.4 hardcodes the expected RS256 algorithm instead of trusting the JWT header, and replaces the Google adapter's custom key fetcher with jwks-rsa which rejects unknown key IDs. As a workaround, dsable Google authentication until upgrading is possible.
— NVD
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-27804?
CVE-2026-27804 is considered a critical vulnerability due to its potential for account takeover.
How do I fix CVE-2026-27804?
To fix CVE-2026-27804, upgrade to Parse Server version 8.6.3 or 9.3.1-alpha.4 or later.
Who is affected by CVE-2026-27804?
CVE-2026-27804 affects deployments of Parse Server using Google authentication versions up to 8.6.2 and between 9.0.0 and 9.3.1-alpha.3.
What type of attack is associated with CVE-2026-27804?
CVE-2026-27804 is associated with an account takeover attack via JWT algorithm confusion.
Can CVE-2026-27804 be exploited without authentication?
Yes, CVE-2026-27804 can be exploited by an unauthenticated attacker to log in as any user linked to a Google account.