Rack: Content-Length mismatch in Rack::Files error responses_CVE-2026-34831

4.8 / 10

MEDIUM

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Description

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.

Basic Information

ID CVE-2026-34831

Source GitHub_M

Published Apr 2, 2026 at 16:43

Modified Apr 3, 2026 at 17:48

Affected Product

Vendor rack

Product rack

Version < 2.2.23

Affected Versions rack rack < 2.2.23
rack rack >= 3.0.0.beta1, < 3.1.21
rack rack >= 3.2.0, < 3.2.6

CWE Classification

CWE-130 CWE-135

References

github.com /rack/rack/security/advisories/GHSA-q2ww-5357-x388

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