In short
- CVE-2025-61772 is a HIGH (CVSS 7.5) vulnerability affecting rack, rack (rack).
- Chance of exploitation in the next 30 days (EPSS): 0.93%, higher than 60.6% of all vulnerabilities.
- Fix: update to 3.1.17, 3.2.2, 2.2.19 or later.
| Package | Affected versions | Patched versions |
|---|
| rack RubyGems | ≥ 3.1, < 3.1.17≥ 3.2, < 3.2.2< 2.2.19
| 3.1.173.2.22.2.19
|
| rack | ≥ 3.1.0, < 3.1.17≥ 3.2.0, < 3.2.2< 2.2.19
| 3.1.173.2.22.2.19
|
Description
Summary
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.
Impact
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.
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).
NVD description
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`).
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