{"cve":"CVE-2026-34835","nvd":{"published":"2026-04-02T18:16:33.967","modified":"2026-07-24T21:10:00.143","status":"Analyzed","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N","score":6.5},"cwes":["CWE-1286"],"references":["https://github.com/rack/rack/security/advisories/GHSA-g2pf-xv49-m2h5"],"products":["rack:rack"],"source":"nvd","synced_at":"2026-10-19T22:28:18.033120106+00:00"},"epss":{"cve":"CVE-2026-34835","score":0.002,"percentile":0.09845,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-g2pf-xv49-m2h5","url":"https://osv.dev/vulnerability/GHSA-g2pf-xv49-m2h5","summary":"Rack::Request accepts invalid Host characters, enabling host allowlist bypass","modified":"2026-09-10T03:50:44.295660719Z","packages":[{"ecosystem":"RubyGems","name":"rack","purl":"pkg:gem/rack","ranges":[">=3.0.0.beta1 <3.1.21"],"fixed":["3.1.21"]},{"ecosystem":"RubyGems","name":"rack","purl":"pkg:gem/rack","ranges":[">=3.2.0 <3.2.6"],"fixed":["3.2.6"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}