CVE-2026-34829 — Rack: Denial of Service via Unbounded Multipart File Upload Without Content-Length

Affected: rack, Red Hat Logging Subsystem for Red Hat OpenShift, Red Hat 3scale API Management Platform 2, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9

Rack 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 BoundedIO when CONTENT_LENGTH is present. When a multipart/form-data request is sent without a Content-Length header, such as with HTTP chunked transfer encoding, multipart parsing continues until end-of-stream with no total size limit. For file parts, the uploaded body is written directly to a temporary file on disk rather than being constrained by the buffered in-memory upload limit. An unauthenticated attacker can therefore stream an arbitrarily large multipart file upload and consume unbounded disk space. This results in a denial of service condition for Rack applications that accept multipart form data. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

USN-8182-1 — ruby-rack vulnerabilities

Affected: Ubuntu:Pro:14.04:LTS: ruby-rack, Ubuntu:Pro:16.04:LTS: ruby-rack, Ubuntu:Pro:18.04:LTS: ruby-rack, Ubuntu:Pro:20.04:LTS: ruby-rack, Ubuntu:Pro:22.04:LTS: ruby-rack, Ubuntu:24.04:LTS: ruby-rack, Ubuntu:25.10: ruby-rack

Andrew Lacambra discovered that Rack did not properly parse certain regular expressions. An attacker could possibly use this issue to bypass network security filters. This issue only affected Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 25.10. (CVE-2026-26961)

William T. Nelson discovered that Rack did not handle multipart headers correctly. An attacker could possibly use this issue to cause downstream parsing issues or a denial of service. This issue only affected Ubuntu 25.10. (CVE-2026-26962)

It was discovered that Rack did not handle the Forwarded header correctly. An attacker could possibly use this issue to manipulate header values. This issue only affected Ubuntu 25.10. (CVE-2026-32762)

It was discovered that Rack could consume excessive CPU when handling certain Accept-Encoding values. An attacker could possibly use this issue to cause a denial of service. (CVE-2026-34230)

Haruki Oyama discovered that certain configurations of Rack could erroneously fail to derive the displayed directory path, and expose the full filesystem path. An attacker could possibly use this issue to disclose deployment details such as layout and usernames. (CVE-2026-34763)

It was discovered that Rack did not properly handle static file paths. An attacker could possibly use this issue to exfiltrate unintentionally served data. (CVE-2026-34785)

Haruki Oyama discovered that Rack did not apply header rules to certain requests for URL-encoded static paths. An attacker cou…

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CVE-2026-34829 — Rack: Denial of Service via Unbounded Multipart File Upload Without Content-Length

USN-8182-1 — ruby-rack vulnerabilities