CVE-2025-61919

Rack::Request#POST reads the entire request body into memory for Content-Type: application/x-www-form-urlencoded, calling rack.input.read(nil) without enforcing a length or cap. Large request bodies can therefore be buffered completely into process memory before parsing, leading to denial of service (DoS) through memory exhaustion.

Details

When handling non-multipart form submissions, Rack’s request parser performs:

form_vars = get_header(RACK_INPUT).read

Since read is called with no argument, the entire request body is loaded into a Ruby String. This occurs before query parameter parsing or enforcement of any params_limit. As a result, Rack applications without an upstream body-size limit can experience unbounded memory allocation proportional to request size.

Mitigation

• Update to a patched version of Rack that enforces form parameter limits using query_parser.bytesize_limit, preventing unbounded reads of application/x-www-form-urlencoded bodies.
• Enforce strict maximum body size at the proxy or web server layer (e.g., Nginx client_max_body_size, Apache LimitRequestBody).

Attackers can send large application/x-www-form-urlencoded bodies to consume process memory, causing slowdowns or termination by the operating system (OOM). The effect scales linearly with request size and concurrency. Even with parsing limits configured, the issue occurs before those limits are enforced.

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2025-61919 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.2.20, 3.1.18, 3.2.3); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-61919? CVE-2025-61919 is a high-severity uncontrolled resource consumption vulnerability in rack (rubygems), affecting versions < 2.2.20. It is fixed in 2.2.20, 3.1.18, 3.2.3. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2025-61919? CVE-2025-61919 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of rack are affected by CVE-2025-61919? rack (rubygems) versions < 2.2.20 is affected.
4. Is there a fix for CVE-2025-61919? Yes. CVE-2025-61919 is fixed in 2.2.20, 3.1.18, 3.2.3. Upgrade to this version or later.
5. Is CVE-2025-61919 exploitable, and should I be worried? Whether CVE-2025-61919 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-61919 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-61919?
   • Upgrade rack to 2.2.20 or later
   • Upgrade rack to 3.1.18 or later
   • Upgrade rack to 3.2.3 or later