Rack up to 2.2.22/3.1.20/3.2.5 Content-Type Header Rack::Multipart interpretation conflict

Summaryinfo

A vulnerability was found in Rack up to 2.2.22/3.1.20/3.2.5. It has been classified as problematic. Affected is the function Rack::Multipart of the component Content-Type Header Handler. The manipulation leads to interpretation conflict. This vulnerability is uniquely identified as CVE-2026-26961. The attack is possible to be carried out remotely. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in Rack up to 2.2.22/3.1.20/3.2.5 and classified as problematic. This issue affects the function Rack::Multipart of the component Content-Type Header Handler. The manipulation with an unknown input leads to a interpretation conflict vulnerability. Using CWE to declare the problem leads to CWE-436. Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state. Impacted is integrity. The summary by CVE is:

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.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-26961 since 02/16/2026. The exploitation is known to be difficult. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 2.2.23, 3.1.21 or 3.2.6 eliminates this vulnerability.

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Name

• Rack

Version

• 2.2.0
• 2.2.1
• 2.2.2
• 2.2.3
• 2.2.4
• 2.2.5
• 2.2.6
• 2.2.7
• 2.2.8
• 2.2.9
• 2.2.10
• 2.2.11
• 2.2.12
• 2.2.13
• 2.2.14
• 2.2.15
• 2.2.16
• 2.2.17
• 2.2.18
• 2.2.19
• 2.2.20
• 2.2.21
• 2.2.22
• 3.1.0
• 3.1.1
• 3.1.2
• 3.1.3
• 3.1.4
• 3.1.5
• 3.1.6
• 3.1.7
• 3.1.8
• 3.1.9
• 3.1.10
• 3.1.11
• 3.1.12
• 3.1.13
• 3.1.14
• 3.1.15
• 3.1.16
• 3.1.17
• 3.1.18
• 3.1.19
• 3.1.20
• 3.2.0
• 3.2.1
• 3.2.2
• 3.2.3
• 3.2.4
• 3.2.5

Website

• Product: https://github.com/rack/rack/

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