Stored XSS via malformed CSP nonce reflection
Published May 13, 2026 · Updated May 13, 2026
Stored XSS in Vercel Next.js App Router 13.4.0 through 15.5.15 and 16.0.0 through 16.2.4 allows remote attackers to execute scripts. The renderer reflects malformed nonce values derived from inbound Content-Security-Policy headers into HTML without blocking attribute-context breakout. Exploitation requires a nonce-using App Router deployment behind a shared cache and a later visitor to receive the poisoned response.
Summary
What happened
Stored XSS in Vercel Next.js App Router 13.4.0 through 15.5.15 and 16.0.0 through 16.2.4 allows remote attackers to execute scripts. The renderer reflects malformed nonce values derived from inbound Content-Security-Policy headers into HTML without blocking attribute-context breakout. Exploitation requires a nonce-using App Router deployment behind a shared cache and a later visitor to receive the poisoned response.
The record
- CVE
- CVE-2026-44581
- Published
- May 13, 2026
- Updated
- May 13, 2026
- Vendor
- Vercel
- Product
- Next.js
- Classifications
- CWE-79, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 13, 2026CVE publishedPublication date reported by the CVE source.
- May 13, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=>= 13.4.0, < 15.5.16
- Affected versionversion=>= 16.0.0, < 16.2.5
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
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo