PT-2026-29856 · Rack · Rack

Taiphung217 · Published 2026-04-02 · Updated 2026-04-02 · CVE-2026-34827

Mitre

CVSS v3.1

7.5

High

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

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.

Fix

Resource Exhaustion

Allocation of Resources Without Limits

Weakness Enumeration

CWE-400

CWE-770

CWE-407

Related Identifiers

CVE-2026-34827

Affected Products

Rack

References · 2

• https://nvd.nist.gov/vuln/detail/CVE-2026-34827 · Security Note
• https://github.com/rack/rack/security/advisories/GHSA-v6x5-cg8r-vv6x · Note