CVE-2025-61772

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).

Details

While reading multipart headers, the parser waits for CRLFCRLF using:

@sbuf.scan_until(/(.*?\r\n)\r\n/m)

If the terminator never appears, it continues appending data (@sbuf.concat(content)) indefinitely. There is no limit on accumulated header bytes, so a single malformed part can consume memory proportional to the request body size.

Mitigation

• Upgrade to a patched Rack version that caps per-part header size (e.g., 64 KiB).
• Until then, restrict maximum request sizes at the proxy or web server layer (e.g., Nginx client_max_body_size).

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.

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

CVE-2025-61772 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 (2.2.19, 3.1.17, 3.2.2); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-61772? CVE-2025-61772 is a high-severity uncontrolled resource consumption vulnerability in rack (rubygems), affecting versions < 2.2.19. It is fixed in 2.2.19, 3.1.17, 3.2.2. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2025-61772? CVE-2025-61772 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-2025-61772? rack (rubygems) versions < 2.2.19 is affected.
4. Is there a fix for CVE-2025-61772? Yes. CVE-2025-61772 is fixed in 2.2.19, 3.1.17, 3.2.2. Upgrade to this version or later.
5. Is CVE-2025-61772 exploitable, and should I be worried? Whether CVE-2025-61772 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-2025-61772 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-2025-61772?
   • Upgrade rack to 2.2.19 or later
   • Upgrade rack to 3.1.17 or later
   • Upgrade rack to 3.2.2 or later