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Vulnerability record · CVE-2026-34827 · published 2 April 2026

CVE-2026-34827: Rack uncontrolled resource consumption 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::Multipart::Parser#handle_mime_head parses quoted multipart parameters such as Content-Disposition: form-data; name="..." using repeated String#index searches combined with String#slice! prefix deletion. For escape-heavy quoted values, this causes super-linear processing. An unauthenticated attacker can send a crafted multipart/form-data request containing many parts with long backslash-escaped parameter values to trigger excessive CPU usage during multipart parsing. This results in a denial of service condition in Rack applications that accept multipart form data. This issue has been patched in versions 3.1.21 and 3.2.6.

7.5 CVSS 3.1 High EPSS 0.66% · top 50.5% CWE-400 · Uncontrolled resource consumptionCWE-407 · CWE-407
7.5CVSS 3.1 base score
0.66%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
4References
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::Multipart::Parser#handle_mime_head parses quoted multipart parameters such as Content-Disposition: form-data; name="..." using repeated String#index searches combined with String#slice! prefix deletion. For escape-heavy quoted values, this causes super-linear processing. An unauthenticated attacker can send a crafted multipart/form-data request containing many parts with long backslash-escaped parameter values to trigger excessive CPU usage during multipart parsing. This results in a denial of service condition in Rack applications that accept multipart form data. 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:N/I:N/A:H

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-v6x5-cg8r-vv6x MitigationVendor Advisory
https://access.redhat.com/security/cve/CVE-2026-34827
https://bugzilla.redhat.com/show_bug.cgi?id=2454501
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34827.json

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Related vulnerabilities

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

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%7.5CVE-2025-61771Rack uncontrolled resource consumption vulnerabilityRack is a modular Ruby web server interface. In versions prior to 2.2.19, 3.1.17, and 3.2.2, ``Rack::Multipart::Parser` stores non-file form fields (…EPSS 0.56%

Source: NIST National Vulnerability Database (record CVE-2026-34827), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.