CVE-2026-34831

A flaw was found in Rack. A remote attacker can exploit this vulnerability by requesting a non-existent path containing percent-encoded UTF-8 characters. This causes Rack::Files#fail to incorrectly calculate the Content-Length header, using String#size instead of String#bytesize for multibyte characters. This leads to incorrect HTTP response framing, which may cause response desynchronization in systems relying on the Content-Length value.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.