CVE-2026-9678

undici vulnerable to cross-user information disclosure via shared cache whitespace bypass

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.

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.

CVE-2026-9678 has a CVSS score of 5.9 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (7.28.0, 8.5.0); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Upgrade to undici v7.28.0 or v8.5.0.

1. What is CVE-2026-9678? CVE-2026-9678 is a medium-severity security vulnerability in undici (npm), affecting versions >= 7.0.0, < 7.28.0. It is fixed in 7.28.0, 8.5.0.
2. How severe is CVE-2026-9678? CVE-2026-9678 has a CVSS score of 5.9 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of undici are affected by CVE-2026-9678? undici (npm) versions >= 7.0.0, < 7.28.0 is affected.
4. Is there a fix for CVE-2026-9678? Yes. CVE-2026-9678 is fixed in 7.28.0, 8.5.0. Upgrade to this version or later.
5. Is CVE-2026-9678 exploitable, and should I be worried? Whether CVE-2026-9678 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-9678 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-9678?
   • Upgrade undici to 7.28.0 or later
   • Upgrade undici to 8.5.0 or later

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