EUVD-2026-11685
GHSA-2mjp-6q6p-2qxm
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
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4Tags
Description
Undici allows duplicate HTTP Content-Length headers when they are provided in an array with case-variant names (e.g., Content-Length and content-length). This produces malformed HTTP/1.1 requests with multiple conflicting Content-Length values on the wire. Who is impacted: * Applications using undici.request(), undici.Client, or similar low-level APIs with headers passed as flat arrays * Applications that accept user-controlled header names without case-normalization Potential consequences: * Denial of Service: Strict HTTP parsers (proxies, servers) will reject requests with duplicate Content-Length headers (400 Bad Request) * HTTP Request Smuggling: In deployments where an intermediary and backend interpret duplicate headers inconsistently (e.g., one uses the first value, the other uses the last), this can enable request smuggling attacks leading to ACL bypass, cache poisoning, or credential hijacking
Analysis
Undici fails to normalize HTTP header names when processing arrays, allowing duplicate Content-Length headers with case-variant names (e.g., "Content-Length" and "content-length") to be sent in malformed requests. Applications using undici's low-level APIs with user-controlled header inputs are vulnerable to request rejection by strict HTTP parsers or potential HTTP request smuggling attacks if intermediaries and backend servers interpret conflicting header values inconsistently. …
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Remediation
Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Monitor vendor channels for patch availability.
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