CVE-2025-61772 — Rack's multipart parser buffers unbounded per-part headers, enabling DoS (memory exhaustion)

Affected: rack

Rack is a modular Ruby web server interface. In versions prior to 2.2.19, 3.1.17, and 3.2.2, `Rack::Multipart::Parser` can accumulate unbounded data when a multipart part’s header block never terminates with the required blank line (`CRLFCRLF`). The parser keeps appending incoming bytes to memory without a size cap, allowing a remote attacker to exhaust memory and cause a denial of service (DoS). Attackers can send incomplete multipart headers to trigger high memory use, leading to process termination (OOM) or severe slowdown. The effect scales with request size limits and concurrency. All applications handling multipart uploads may be affected. Versions 2.2.19, 3.1.17, and 3.2.2 cap per-part header size (e.g., 64 KiB). As a workaround, restrict maximum request sizes at the proxy or web server layer (e.g., Nginx `client_max_body_size`).

USN-7960-1 — ruby-rack vulnerabilities

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

It was discovered that Rack incorrectly handled certain query parameters. An attacker could possibly use this issue to cause a limited denial of service. This issue was only addressed in Ubuntu 20.04 LTS and Ubuntu 22.04 LTS. (CVE-2025-59830)

It was discovered that Rack did not properly handle certain multipart form data. An attacker could possibly use this issue to cause memory exhaustion, leading to a denial of service. This issue was only addressed in Ubuntu 22.04 LTS, Ubuntu 24.04 LTS and Ubuntu 25.10. (CVE-2025-61770, CVE-2025-61772)

It was discovered that Rack did not properly handle certain form fields. An attacker could possibly use this issue to cause memory exhaustion, leading to a denial of service. This issue was only addressed in Ubuntu 22.04 LTS, Ubuntu 24.04 LTS and Ubuntu 25.10. (CVE-2025-61771)

It was discovered that Rack did not properly handle certain headers. An attacker could possibly use this issue to bypass proxy access restrictions and obtain sensitive information. (CVE-2025-61780)

Tomoya Yamashita discovered that Rack did not properly manage memory under certain circumstances. An attacker could possibly use this issue to cause memory exhaustion, leading to a denial of service. This issue was only addressed in Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS and Ubuntu 25.10. (CVE-2025-61919)

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CVE-2025-61772 — Rack's multipart parser buffers unbounded per-part headers, enabling DoS (memory exhaustion)

USN-7960-1 — ruby-rack vulnerabilities