CVE-2025-61771 — Rack's multipart parser buffers large non‑file fields entirely in memory, 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` stores non-file form fields (parts without a `filename`) entirely in memory as Ruby `String` objects. A single large text field in a multipart/form-data request (hundreds of megabytes or more) can consume equivalent process memory, potentially leading to out-of-memory (OOM) conditions and denial of service (DoS). Attackers can send large non-file fields to trigger excessive memory usage. Impact scales with request size and concurrency, potentially leading to worker crashes or severe garbage-collection overhead. All Rack applications processing multipart form submissions are affected. Versions 2.2.19, 3.1.17, and 3.2.2 enforce a reasonable size cap for non-file fields (e.g., 2 MiB). Workarounds include restricting maximum request body size at the web-server or proxy layer (e.g., Nginx `client_max_body_size`) and validating and rejecting unusually large form fields at the application level.

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)

Most recent entries from all

CVE-2025-61771 — Rack's multipart parser buffers large non‑file fields entirely in memory, enabling DoS (memory exhaustion)

USN-7960-1 — ruby-rack vulnerabilities