GHSA-4633-3j49-mh5q: Next.js: Cache confusion of response bodies for requests with bodies containing invalid UTF-8 byte sequences

mediumCVE-2026-64647

Impact 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. Workarounds If you cannot upgrade, consider only making fetch requests with UTF-8 bodies (default in Next.js). Applications using Pages Router are not vulnerable.

Details

Source: GitHub Security Advisories (INTL · database · site)
Severity: medium
Published: 2026-07-22
Last updated: 2026-07-22
Exploitation: Not in CISA KEV at last sync

Original advisory: https://github.com/advisories/GHSA-4633-3j49-mh5q

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-646470.34% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 26% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-64647	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

GHSA-4633-3j49-mh5q: Next.js: Cache confusion of response bodies for requests with bodies containing invalid UTF-8 byte sequences

Details

Exploitation outlook

Referenced CVEs

Same CVEs, other sources

More from GitHub Security Advisories