CVE-2026-34831

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.

CVSS v3 4.8 MEDIUM

4.8^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.2 / Impact : 2.5

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required NONE

User Interaction NONE

Confidentiality Impact LOW

Integrity Impact LOW

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388	Vendor Advisory

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:rack:rack::::::ruby::*
	cpe:2.3:a:rack:rack::::::ruby::*
	cpe:2.3:a:rack:rack::::::ruby::*

History

16 Apr 2026, 16:44

Type	Values Removed	Values Added
References	~~() https://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388 -~~	() https://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388 - Vendor Advisory
CPE		cpe:2.3:a:rack:rack::::::ruby::*
First Time		Rack rack Rack

02 Apr 2026, 17:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-04-02 17:16

Updated : 2026-04-16 16:44

NVD link : CVE-2026-34831

Mitre link : CVE-2026-34831

CVE.ORG link : CVE-2026-34831

JSON object : View

Products Affected

rack

rack

CWE

CWE-130

Improper Handling of Length Parameter Inconsistency

CWE-135

Incorrect Calculation of Multi-Byte String Length

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