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Vulnerability record · CVE-2026-34835 · published 2 April 2026

CVE-2026-34835: Rack vulnerability

Rack · Rack

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.

6.5 CVSS 3.1 Medium EPSS 0.28% · top 81.7% CWE-1286 · CWE-1286
6.5CVSS 3.1 base score
0.28%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
1References, 1 tagged exploit
24 Jul 2026Last modified by NVD

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:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/rack/rack/security/advisories/GHSA-g2pf-xv49-m2h5 ExploitMitigationVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

7.5CVE-2026-34827Rack uncontrolled resource consumption vulnerabilityRack 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::Multipart::Parser#handle_mi…EPSS 0.66%7.5CVE-2026-34829Rack uncontrolled resource consumption vulnerabilityRack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Multipart::Parser only wraps the request body in a Bo…EPSS 0.66%7.5CVE-2026-34830Rack vulnerabilityRack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Sendfile#map_accel_path interpolates the value of the…EPSS 0.40%7.5CVE-2026-34826Rack uncontrolled resource consumption vulnerabilityRack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Utils.get_byte_ranges parses the HTTP Range header wi…EPSS 0.46%7.5CVE-2026-34785Rack information exposure vulnerabilityRack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Static determines whether a request should be served …EPSS 0.52%7.5CVE-2026-34230Rack uncontrolled resource consumption vulnerabilityRack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Utils.select_best_encoding processes Accept-Encoding …EPSS 0.48%7.5CVE-2026-22860Rack path traversal vulnerabilityRack is a modular Ruby web server interface. Prior to versions 2.2.22, 3.1.20, and 3.2.5, `Rack::Directory`’s path check used a string prefix match o…EPSS 0.68%7.5CVE-2025-61919Rack uncontrolled resource consumption vulnerabilityRack is a modular Ruby web server interface. Prior to versions 2.2.20, 3.1.18, and 3.2.3, `Rack::Request#POST` reads the entire request body into mem…EPSS 0.65%

Source: NIST National Vulnerability Database (record CVE-2026-34835), CISA KEV, FIRST EPSS (scores of 2026-10-01). This page is refreshed as NVD updates the record.