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Low severity3.7NVD Advisory· Published Apr 2, 2026· Updated Apr 16, 2026

CVE-2026-26961

CVE-2026-26961

Description

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.

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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

65

Patches

Vulnerability mechanics

References

4

News mentions

0

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