Information disclosure due to improper cache-control header parsing

Summary

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. A flaw was found in Undici. The cache interceptor in shared-cache mode incorrectly classifies certain responses as cacheable due to improper handling of whitespace-padded Cache-Control header field names. This vulnerability allows an unauthenticated attacker to access authenticated user data from the cache, leading to information disclosure. This occurs when both authenticated and unauthenticated requests resolve to the same cache key. This Moderate information disclosure flaw in Undici's cache interceptor, when configured in shared-cache mode, allows an unauthenticated attacker to retrieve sensitive authenticated user data. This is due to incorrect parsing of Cache-Control headers containing whitespace-padded field names, leading to cached responses being served improperly. Red Hat products are affected if they explicitly enable shared-cache mode, forward Authorization headers, and process non-canonical Cache-Control directives. Red Hat severity: Moderate — CVSS 5.9 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N). Weakness: CWE-1286. Fixed by RHSA-2026:35841, RHSA-2026:35842, RHSA-2026:22380, RHSA-2026:7378 — update the affected packages (`sudo dnf update`). Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Hardened Images.