Rack up to 3.1.20/3.2.5 Web Server Interface Rack::Utils interpretation conflict

Summaryinfo

A vulnerability labeled as problematic has been found in Rack up to 3.1.20/3.2.5. This issue affects the function Rack::Utils of the component Web Server Interface. Executing a manipulation can lead to interpretation conflict. This vulnerability is tracked as CVE-2026-32762. The attack can be launched remotely. No exploit exists. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as problematic was found in Rack up to 3.1.20/3.2.5. This vulnerability affects the function Rack::Utils of the component Web Server Interface. The manipulation with an unknown input leads to a interpretation conflict vulnerability. The CWE definition for the vulnerability is 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. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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::Utils.forwarded_values parses the RFC 7239 Forwarded header by splitting on semicolons before handling quoted-string values. Because quoted values may legally contain semicolons, a header can be interpreted by Rack as multiple Forwarded directives rather than as a single quoted for value. In deployments where an upstream proxy, WAF, or intermediary validates or preserves quoted Forwarded values differently, this discrepancy can allow an attacker to smuggle host, proto, for, or by parameters through a single header value. This issue has been patched in versions 3.1.21 and 3.2.6.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-32762 since 03/13/2026. The exploitation appears to be difficult. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available.

Upgrading to version 3.1.21 or 3.2.6 eliminates this vulnerability.

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Productinfo

Name

• Rack

Version

• 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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