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CVE-2026-34835— Rack: `Rack::Request` accepts invalid Host characters, enabling host allowlist bypass.

CVSS 4.8 · Medium EPSS 0.11% · P29
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I. Basic Information for CVE-2026-34835

Vulnerability Information
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Vulnerability Title
Rack: `Rack::Request` accepts invalid Host characters, enabling host allowlist bypass.
Source: NVD (National Vulnerability Database)
Vulnerability 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.
Source: NVD (National Vulnerability Database)
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
Source: NVD (National Vulnerability Database)
Vulnerability Type
CWE-1286
Source: NVD (National Vulnerability Database)
Vulnerability Title
Rack 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Rack是Rack开源的一个模块化的Ruby web服务器界面。 Rack 3.1.21之前版本和3.2.6之前版本存在安全漏洞，该漏洞源于Rack::Request使用AUTHORITY正则表达式解析Host标头时接受非法字符，可能导致主机标头投毒。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

VendorProductAffected VersionsCPESubscribe
rackrack >= 3.0.0.beta1, < 3.1.21 -

II. Public POCs for CVE-2026-34835

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III. Intelligence Information for CVE-2026-34835

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Same Patch Batch · rack · 2026-04-02 · 13 CVEs total

CVE-2026-347857.5 HIGHRack: Local file inclusion in `Rack::Static` via URL Prefix Matching
CVE-2026-348277.5 HIGHRack: Algorithmic-Complexity DoS in Rack::Multipart::Parser
CVE-2026-348297.5 HIGHRack: Denial of Service via Unbounded Multipart File Upload Without Content-Length
CVE-2026-348305.9 MEDIUMRack: Rack::Sendfile regex injection via HTTP_X_ACCEL_MAPPING header allows arbitrary file
CVE-2026-348265.3 MEDIUMRack: Unbounded Range Count in get_byte_ranges Enables DoS
CVE-2026-347865.3 MEDIUMRack: Rack::Static header_rules bypass via URL-encoded paths
CVE-2026-347635.3 MEDIUMRack: Rack::Directory info disclosure and DoS via unescaped regex interpolation
CVE-2026-342305.3 MEDIUMRack: Quadratic complexity in Rack::Utils.select_best_encoding via wildcard Accept-Encodin
CVE-2026-269624.8 MEDIUMRack: Header injection in multipart requests
CVE-2026-327624.8 MEDIUMRack: Forwarded Header semicolon injection enables Host and Scheme spoofing
CVE-2026-348314.8 MEDIUMRack: Content-Length mismatch in Rack::Files error responses
CVE-2026-269613.7 LOWRack: Multipart Boundary Parsing Ambiguity allowing WAF Bypass

IV. Related Vulnerabilities

Same product: rack
Same vendor: rack
Same weakness: CWE-1286

V. Comments for CVE-2026-34835

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