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Medium severity4.8NVD Advisory· Published Apr 2, 2026· Updated Apr 16, 2026

CVE-2026-34831

CVE-2026-34831

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.

AI Insight

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
rackRubyGems
< 2.2.232.2.23
rackRubyGems
>= 3.0.0.beta1, < 3.1.213.1.21
rackRubyGems
>= 3.2.0, < 3.2.63.2.6

Affected products

60

Patches

Vulnerability mechanics

References

4

News mentions

0

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