Rack up to 2.2.22/3.1.20/3.2.5 Response Header Rack::Files Content-Length length parameter

Summaryinfo

A vulnerability was found in Rack up to 2.2.22/3.1.20/3.2.5 and classified as problematic. This impacts the function Rack::Files of the component Response Header Handler. Executing a manipulation of the argument Content-Length can lead to length parameter. This vulnerability is handled as CVE-2026-34831. The attack can be executed remotely. There is not any exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability has been found in Rack up to 2.2.22/3.1.20/3.2.5 and classified as problematic. This vulnerability affects the function Rack::Files of the component Response Header Handler. The manipulation of the argument Content-Length with an unknown input leads to a length parameter vulnerability. The CWE definition for the vulnerability is CWE-130. The product parses a formatted message or structure, but it does not handle or incorrectly handles a length field that is inconsistent with the actual length of the associated data. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than the number of bytes actually sent on the wire. Because Rack::Files reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters. This results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect Content-Length value. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

The advisory is available at github.com. This vulnerability was named CVE-2026-34831 since 03/30/2026. The exploitation appears to be difficult. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit.

Upgrading to version 2.2.23, 3.1.21 or 3.2.6 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-18392). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Name

• Rack

Version

• 2.2.0
• 2.2.1
• 2.2.2
• 2.2.3
• 2.2.4
• 2.2.5
• 2.2.6
• 2.2.7
• 2.2.8
• 2.2.9
• 2.2.10
• 2.2.11
• 2.2.12
• 2.2.13
• 2.2.14
• 2.2.15
• 2.2.16
• 2.2.17
• 2.2.18
• 2.2.19
• 2.2.20
• 2.2.21
• 2.2.22
• 3.1.0
• 3.1.1
• 3.1.2
• 3.1.3
• 3.1.4
• 3.1.5
• 3.1.6
• 3.1.7
• 3.1.8
• 3.1.9
• 3.1.10
• 3.1.11
• 3.1.12
• 3.1.13
• 3.1.14
• 3.1.15
• 3.1.16
• 3.1.17
• 3.1.18
• 3.1.19
• 3.1.20
• 3.2.0
• 3.2.1
• 3.2.2
• 3.2.3
• 3.2.4
• 3.2.5

Website

• Product: https://github.com/rack/rack/

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If you want to get best quality of vulnerability data, you may have to visit VulDB.

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