CVE-2026-34230— Rack: Quadratic complexity in Rack::Utils.select_best_encoding via wildcard Accept-Encoding header
Quick assessment
Affected
rack rack
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
Rack是Rack开源的一个模块化的Ruby web服务器界面。 Rack 2.2.23之前版本、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::Utils.select_best_encoding处理包含大量通配符条目的Accept-Encoding标头时具有二次时间复杂度，可能导致CPU消耗过高，进而引发拒绝服务攻击。
Possible ATT&CK Techniques 1 AI
T1499 · Endpoint Denial of Service
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I. Basic Information for CVE-2026-34230
Vulnerability Information
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Vulnerability Title
Rack: Quadratic complexity in Rack::Utils.select_best_encoding via wildcard Accept-Encoding header
Source: CVE Program / CVE List V5
Vulnerability Description
Rack 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 values with quadratic time complexity when the header contains many wildcard (*) entries. Because this method is used by Rack::Deflater to choose a response encoding, an unauthenticated attacker can send a single request with a crafted Accept-Encoding header and cause disproportionate CPU consumption on the compression middleware path. This results in a denial of service condition for applications using Rack::Deflater. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5
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 2.2.23之前版本、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::Utils.select_best_encoding处理包含大量通配符条目的Accept-Encoding标头时具有二次时间复杂度，可能导致CPU消耗过高，进而引发拒绝服务攻击。
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
II. Public POCs for CVE-2026-34230
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Vendor Advisories for CVE-2026-34230 (1)
Same Patch Batch · rack · 2026-04-02 · 13 CVEs total
| CVE-2026-34785 | 7.5 HIGH | Rack: Local file inclusion in `Rack::Static` via URL Prefix Matching |
| CVE-2026-34827 | 7.5 HIGH | Rack: Algorithmic-Complexity DoS in Rack::Multipart::Parser |
| CVE-2026-34829 | 7.5 HIGH | Rack: Denial of Service via Unbounded Multipart File Upload Without Content-Length |
| CVE-2026-34830 | 5.9 MEDIUM | Rack: Rack::Sendfile regex injection via HTTP_X_ACCEL_MAPPING header allows arbitrary file |
| CVE-2026-34826 | 5.3 MEDIUM | Rack: Unbounded Range Count in get_byte_ranges Enables DoS |
| CVE-2026-34786 | 5.3 MEDIUM | Rack: Rack::Static header_rules bypass via URL-encoded paths |
| CVE-2026-34763 | 5.3 MEDIUM | Rack: Rack::Directory info disclosure and DoS via unescaped regex interpolation |
| CVE-2026-26962 | 4.8 MEDIUM | Rack: Header injection in multipart requests |
| CVE-2026-32762 | 4.8 MEDIUM | Rack: Forwarded Header semicolon injection enables Host and Scheme spoofing |
| CVE-2026-34835 | 4.8 MEDIUM | Rack: `Rack::Request` accepts invalid Host characters, enabling host allowlist bypass. |
| CVE-2026-34831 | 4.8 MEDIUM | Rack: Content-Length mismatch in Rack::Files error responses |
| CVE-2026-26961 | 3.7 LOW | Rack: Multipart Boundary Parsing Ambiguity allowing WAF Bypass |
IV. Related Vulnerabilities
Same product: rack
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CVE-2026-26962
Rack: Header injection in multipart requests -
CVE-2026-34835
Rack: `Rack::Request` accepts invalid Host characters, enabl -
CVE-2026-34827
Rack: Algorithmic-Complexity DoS in Rack::Multipart::Parser -
CVE-2026-32762
Rack: Forwarded Header semicolon injection enables Host and -
CVE-2026-34830
Rack: Rack::Sendfile regex injection via HTTP_X_ACCEL_MAPPIN
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CVE-2026-34827
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CVE-2026-32762
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Same weakness: CWE-400
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V. Comments for CVE-2026-34230
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