CVE-2026-9678: undici vulnerable to cross-user information disclosure via shared cache whitespace bypass

Vulnerability summary

CVE-2026-9678 is a medium (CVSS 5.9) vulnerability in nodejs undici. EPSS estimates a 0.39% chance of exploitation in the next 30 days, higher than 33% of scored vulnerabilities.

Timeline

1. 17-06-2026
   PublishedVulnerability first disclosed.
2. 17-06-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-524Use of Cache Containing Sensitive InformationThe code uses a cache that contains sensitive information, but the cache can be read by an actor outside of the intended control sphere.