CVE-2026-91920

Undertow: undertow: chunkreader message length permits chunk-size overflow

CVSS 3.1 6.5 MEDIUMCheck source for fixed versionsKEV status unknown

Original advisory

cve-program · CVE-2026-91920

Published

A flaw was found in the ChunkReader component of the Undertow web server, which is used to handle chunked transfer encoding in HTTP requests. The issue occurs because a security check for the chunk size is performed before the value is shifted, allowing a specifically crafted 15-digit chunk size to bypass the limit and overflow into internal state flags. This can cause the server to terminate a request body prematurely and interpret the remaining data as a separate, smuggled request.

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Affected versions, risk and source history

Exploitation and risk

Source status

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Risk history

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Advisory history

5 saved versions

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6 Nov 2026 02:36:20 UTC