Cross-site action execution via null-origin misclassification
Published Mar 17, 2026 · Updated Mar 18, 2026
CSRF in Server Action validation in Vercel Next.js 16.0.1 through 16.1.6 allows remote attackers to submit actions as a victim. The action handler converts the explicit Origin value null to an absent origin, so host comparison and the cross-origin rejection path are skipped. Exploitation requires a victim with applicable credentials to load attacker-controlled content in an opaque context, such as a sandboxed iframe, and can execute state-changing Server Actions under that victim's session.
Summary
What happened
CSRF in Server Action validation in Vercel Next.js 16.0.1 through 16.1.6 allows remote attackers to submit actions as a victim. The action handler converts the explicit Origin value null to an absent origin, so host comparison and the cross-origin rejection path are skipped. Exploitation requires a victim with applicable credentials to load attacker-controlled content in an opaque context, such as a sandboxed iframe, and can execute state-changing Server Actions under that victim's session.
The record
- CVE
- CVE-2026-27978
- Published
- Mar 17, 2026
- Updated
- Mar 18, 2026
- Vendor
- Vercel
- Product
- Next.js
- Classifications
- CWE-352
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 17, 2026CVE publishedPublication date reported by the CVE source.
- Mar 18, 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=>= 16.0.1, < 16.1.7
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
- Next.js CVE-2026-27978 proof-of-concept environmentproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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