GHSA-8436-99hf-9mmv: Low severity npm/undici vulnerability
Impact
undici's interceptors.cache() documents that it caches only safe HTTP methods. However, its internal skip-list is built by subtracting the configured methods from the safe-methods set, so an unsafe method (POST, PUT, PATCH, DELETE) never lands in the skip-list and is looked up against the cache store. Combined with the storage gate (canCacheResponse) having no method check, a heuristically-cacheable response (for example a 404) with an explicit Cache-Control: max-age=... to an unsafe method is stored and replayed on a subsequent identical request. The application's state-changing request never reaches the origin, and undici serves a fabricated response from the cache instead. This occurs with the default configuration (methods: ['GET']), which the public API does not allow widening to unsafe methods, so no application misuse is required; an untrusted origin can trigger it purely through its own response headers.
Patches
Upgrade to 7.29.1 or 8.10.2. The cache interceptor no longer reads from or writes to the cache for unsafe HTTP methods, while still invalidating existing cache entries on successful unsafe requests.
Workarounds
None.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/undicito a version that resolves this vulnerability.Fixed in 8.10.2 - Upgrade
Upgrade
npm/undicito a version that resolves this vulnerability.Fixed in 7.29.1
Event History
Frequently Asked Questions
Which deployments are exposed?
Applications using undici's interceptors.cache() are affected, including those using its default methods setting of ['GET']. The issue does not require an application to configure unsafe methods for caching.
What does an attacker need to exploit this?
An attacker needs to control an origin response to an unsafe HTTP request and return a heuristically cacheable response with explicit Cache-Control: max-age=... directives. A subsequent identical unsafe request can then be served from cache rather than reaching the origin.
What is the operational impact of successful exploitation?
A state-changing request such as POST, PUT, PATCH, or DELETE may not reach the origin. Instead, undici can replay a cached response, causing the application to treat the request as handled while the intended state change does not occur.
How can this be remediated if the cache interceptor is in use?
Upgrade undici to version 7.29.1 or 8.10.2. No workaround is provided.
How can teams determine whether they are affected?
Check whether the application enables undici's interceptors.cache() and whether its installed undici version predates the stated fixed releases. The vulnerable behavior can occur under the default cache-interceptor configuration.