CVE-2026-91920 vulnerability in Red Hat Products
Published on October 30, 2026
Undertow: undertow: chunkreader message length permits chunk-size overflow
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.
Vulnerability Analysis
CVE-2026-91920 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, with no impact on integrity and availability.
Timeline
Reported to Red Hat.
Made public. 55 days later.
Weakness Type
What is a HTTP Request Smuggling Vulnerability?
When malformed or abnormal HTTP requests are interpreted by one or more entities in the data flow between the user and the web server, such as a proxy or firewall, they can be interpreted inconsistently, allowing the attacker to "smuggle" a request to one device without the other device being aware of it.
CVE-2026-91920 has been classified to as a HTTP Request Smuggling vulnerability or weakness.
Products Associated with CVE-2026-91920
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