CVE-2026-9678
MediumCVSS 5.9Exploitation Probability (EPSS)
Low risk24th percentile — higher than 24% of all known CVEs
Summary
A vulnerability in Undici allows incorrect classification of responses as cacheable when Cache-Control headers contain whitespace. This can lead to authenticated user data being served to another user from the cache.
Risk Assessment
Organizations may be exposed to the disclosure of authenticated user data, posing a serious threat to privacy and data security.
Recommendation
It is recommended to upgrade to undici v7.28.0 or v8.5.0. If an upgrade is not possible, disable shared-cache mode for traffic that includes Authorization headers.
Original NVD description (English source)
Impact: Undici's cache interceptor incorrectly classifies some responses as cacheable when the upstream Cache-Control header uses whitespace-padded qualified private or no-cache field names such as private=" authorization" or no-cache="\tauthorization". The parser preserves the surrounding whitespace, so later comparisons against the literal authorization field name fail and the response is stored. In shared-cache mode, this allows a response containing one user's authenticated data to be served from cache to a subsequent caller, including an unauthenticated caller, when both requests resolve to the same cache key. Affected applications are those that explicitly enable the cache interceptor (interceptors.cache()) in shared mode, forward Authorization headers upstream, and receive cacheable responses with non-canonical qualified private or no-cache directives. Patches: Upgrade to undici v7.28.0 or v8.5.0. Workarounds: If upgrade is not immediately possible, disable shared-cache mode for traffic that includes Authorization headers, avoid caching responses to authenticated requests, or add Vary: Authorization upstream.