CVSS 3.1
5.3 mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:NCVE-2026-26961
Medium (5.3) in rack rack. EPSS 0.3% chance of exploitation in the next 30 days. Fixed in rack 2.2.23, 3.1.21, 3.2.6.
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.
Severity
- EPSS
- 0.3% chance of exploitation in the next 30 days; higher than 18% of CVEs (scores of 2026-11-01)
- CWE
- CWE-436
- Published
- Modified
- Record from
- the NVD, synced
Affected
- rack:rack
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-vgpv-f759-9wx3 | RubyGems | rack | <2.2.23 | 2.2.23 |
| GHSA-vgpv-f759-9wx3 | RubyGems | rack | >=3.0.0.beta1 <3.1.21 | 3.1.21 |
| GHSA-vgpv-f759-9wx3 | RubyGems | rack | >=3.2.0 <3.2.6 | 3.2.6 |