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High severity7.5NVD Advisory· Published Apr 2, 2026· Updated Apr 24, 2026

CVE-2026-34827

CVE-2026-34827

Description

Rack is a modular Ruby web server interface. From versions 3.0.0.beta1 to before 3.1.21, and 3.2.0 to before 3.2.6, Rack::Multipart::Parser#handle_mime_head parses quoted multipart parameters such as Content-Disposition: form-data; name="..." using repeated String#index searches combined with String#slice! prefix deletion. For escape-heavy quoted values, this causes super-linear processing. An unauthenticated attacker can send a crafted multipart/form-data request containing many parts with long backslash-escaped parameter values to trigger excessive CPU usage during multipart parsing. This results in a denial of service condition in Rack applications that accept multipart form data. This issue has been patched in versions 3.1.21 and 3.2.6.

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Affected packages

Versions sourced from the GitHub Security Advisory.

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

Affected products

38

Patches

Vulnerability mechanics

References

4

News mentions

0

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