CVSS 3.1
6.5 mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:NCVE-2026-34835
Medium (6.5) in rack rack. EPSS 0.2% chance of exploitation in the next 30 days. Fixed in rack 3.1.21, 3.2.6.
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::Request parses the Host header using an AUTHORITY regular expression that accepts characters not permitted in RFC-compliant hostnames, including /, ?, #, and @. Because req.host returns the full parsed value, applications that validate hosts using naive prefix or suffix checks can be bypassed. This can lead to host header poisoning in applications that use req.host, req.url, or req.base_url for link generation, redirects, or origin validation. This issue has been patched in versions 3.1.21 and 3.2.6.
Severity
- EPSS
- 0.2% chance of exploitation in the next 30 days; higher than 9% of CVEs (scores of 2026-10-31)
- CWE
- CWE-1286
- Published
- Modified
- Record from
- the NVD, synced
Affected
- rack:rack
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-g2pf-xv49-m2h5 | RubyGems | rack | >=3.0.0.beta1 <3.1.21 | 3.1.21 |
| GHSA-g2pf-xv49-m2h5 | RubyGems | rack | >=3.2.0 <3.2.6 | 3.2.6 |