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CVE-2026-26961

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CVE-2026-26961

Published: Apr 2, 2026

Modified: Apr 3, 2026

PUBLISHED

CVSS v3.1

3.7

LOW

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.

VendorProductVersions

rack

rack

affected
< 2.2.23
affected
>= 3.0.0.beta1, < 3.1.21
affected
>= 3.2.0, < 3.2.6

Weaknesses (CWE)

CWE-436

CVSS v3.1 Details

CVSS v3.1 Vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

None

References

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