Recursion identifier disclosure via cross-host header forwarding
Published Apr 2, 2025 · Updated Oct 13, 2025
Information exposure in Next.js 12.3.5, 13.5.9, 14.2.25, and 15.2.3 allows remote attackers to read a recursion identifier. Middleware's fetch wrapper copies the process-wide x-middleware-subrequest-id header to every outbound request without checking that the destination host matches the application. Exploitation requires control of a third-party host fetched by Middleware and applies only to Vercel's recursion-protection implementation; other hosting providers are unaffected.
Summary
What happened
Information exposure in Next.js 12.3.5, 13.5.9, 14.2.25, and 15.2.3 allows remote attackers to read a recursion identifier. Middleware's fetch wrapper copies the process-wide x-middleware-subrequest-id header to every outbound request without checking that the destination host matches the application. Exploitation requires control of a third-party host fetched by Middleware and applies only to Vercel's recursion-protection implementation; other hosting providers are unaffected.
The record
- CVE
- CVE-2025-30218
- Published
- Apr 2, 2025
- Updated
- Oct 13, 2025
- Vendor
- Vercel
- Product
- Next.js
- Classifications
- CWE-200
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 2, 2025CVE publishedPublication date reported by the CVE source.
- Oct 13, 2025Record 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== 12.3.5
- Affected versionversion== 13.5.9
- Affected versionversion== 14.2.25
- Affected versionversion== 15.2.3
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
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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