CVE-2026-26961
Last modified
CVE-2026-26961 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. 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. EPSS estimates a 0.25% chance of exploitation in the next 30 days.
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.
Metrics
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness Enumeration
Affected Software
| Vendor | Product | Versions |
|---|---|---|
| Rack | Rack | < 2.2.23 |
| Rack | Rack | >= 3.0.0, < 3.1.21 |
| Rack | Rack | >= 3.2.0, < 3.2.6 |
References
Timeline
- Published
- Last Modified
- Status
- Analyzed
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