CVE-2026-64647: CWE-116: Improper Encoding or Escaping of Output in vercel next.js
Next.js is a React framework for building full-stack web applications. In versions 12.0.0 through 15.5.20 and 16.0.0 through 16.2.10, a server-side fetch with a request body may return a cached response body from a different request to the same URL but different body. Confidential data in the POST's response body would then leak to unauthorized requests. Though the request itself will not be deduped. This is only an issue when receiving request bodies with a content type charset other than UTF-8. For example, the UTF-16 byte sequences for 삃삃 and 섄섄 in the request body would share the same cache. This issue has been fixed in versions 15.5.21 and 16.2.11.
AI Analysis
Technical Summary
CVE-2026-64647 affects the Next.js React framework in versions >=13.0.0 <15.5.21 and >=16.0.0 <16.2.11. When a server-side fetch is performed with a request body containing a charset other than UTF-8, the caching mechanism may incorrectly serve a cached response body from a different request to the same URL but with a different request body. This causes confidential data leakage in POST response bodies. The request itself is not deduplicated, but the response cache key does not account properly for the charset encoding, leading to cache collisions. The vulnerability is classified under CWE-116 (Improper Encoding or Escaping of Output).
Potential Impact
Confidential data from POST response bodies may be leaked to unauthorized requests due to improper caching behavior when request bodies use non-UTF-8 charsets. This can expose sensitive information to unintended recipients. The vulnerability has a CVSS 4.0 score of 6.3 (medium severity), indicating a moderate risk with network attack vector, high attack complexity, and partial impact on confidentiality and integrity.
Mitigation Recommendations
Upgrade Next.js to version 15.5.21 or later if using the 13.x to 15.x series, or to version 16.2.11 or later if using the 16.x series. These versions contain the official fix for this caching issue. No other mitigations are indicated by the vendor advisory.
CVE-2026-64647: CWE-116: Improper Encoding or Escaping of Output in vercel next.js
Description
Next.js is a React framework for building full-stack web applications. In versions 12.0.0 through 15.5.20 and 16.0.0 through 16.2.10, a server-side fetch with a request body may return a cached response body from a different request to the same URL but different body. Confidential data in the POST's response body would then leak to unauthorized requests. Though the request itself will not be deduped. This is only an issue when receiving request bodies with a content type charset other than UTF-8. For example, the UTF-16 byte sequences for 삃삃 and 섄섄 in the request body would share the same cache. This issue has been fixed in versions 15.5.21 and 16.2.11.
CVSS v4.0
Score 6.3medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-64647 affects the Next.js React framework in versions >=13.0.0 <15.5.21 and >=16.0.0 <16.2.11. When a server-side fetch is performed with a request body containing a charset other than UTF-8, the caching mechanism may incorrectly serve a cached response body from a different request to the same URL but with a different request body. This causes confidential data leakage in POST response bodies. The request itself is not deduplicated, but the response cache key does not account properly for the charset encoding, leading to cache collisions. The vulnerability is classified under CWE-116 (Improper Encoding or Escaping of Output).
Potential Impact
Confidential data from POST response bodies may be leaked to unauthorized requests due to improper caching behavior when request bodies use non-UTF-8 charsets. This can expose sensitive information to unintended recipients. The vulnerability has a CVSS 4.0 score of 6.3 (medium severity), indicating a moderate risk with network attack vector, high attack complexity, and partial impact on confidentiality and integrity.
Mitigation Recommendations
Upgrade Next.js to version 15.5.21 or later if using the 13.x to 15.x series, or to version 16.2.11 or later if using the 16.x series. These versions contain the official fix for this caching issue. No other mitigations are indicated by the vendor advisory.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-4633-3j49-mh5q
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-64647"]
- Ecosystems
- ["npm"]
- Database Specific Severity
- MODERATE
- Cvss Version
- 4.0
Threat ID: 6a616bcd9c2644c7f80dbd91
Added to database: 07/23/2026, 01:18:05 UTC
Last enriched: 07/30/2026, 15:27:27 UTC
Last updated: 09/05/2026, 10:52:11 UTC
Views: 121
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