PT-2026-29808 · Rack · Rack

Codebymoriarty · Published 2026-04-02 · Updated 2026-04-02 · CVE-2026-26961

Mitre

CVSS v3.1

3.7

Low

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

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Multipart::Parser extracts the boundary parameter from multipart/form-data using a greedy regular expression. When a Content-Type header contains multiple boundary parameters, Rack selects the last one rather than the first. In deployments where an upstream proxy, WAF, or intermediary interprets the first boundary parameter, this mismatch can allow an attacker to smuggle multipart content past upstream inspection and have Rack parse a different body structure than the intermediary validated. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

Fix

Weakness Enumeration

CWE-436

Related Identifiers

CVE-2026-26961

Affected Products

Rack

References · 2

• https://nvd.nist.gov/vuln/detail/CVE-2026-26961 · Security Note
• https://github.com/rack/rack/security/advisories/GHSA-vgpv-f759-9wx3 · Note