CVE-2026-9678
undici vulnerable to cross-user information disclosure via shared cache whitespace bypass
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.
How to fix CVE-2026-9678
To remediate CVE-2026-9678, upgrade the affected package to a fixed version below.
- —no fix listed
- —upgrade to 7.28.0 or later
Is CVE-2026-9678 being exploited?
No exploitation signal available. Neither CISA KEV nor a current EPSS score has been published for CVE-2026-9678.
Affected packages (2)
- from 0
- >= 7.0.0, < 7.28.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| nvd | CVSS 3.1 | MEDIUM5.9 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N |
| osv | CVSS 3.1 | MEDIUM5.9 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N |