CVE-2025-61772 Rack's multipart parser buffers unbounded per-part headers, enabling DoS (memory exhaustion)
Remote attackers can exhaust memory and cause denial of service by sending incomplete multipart headers to Rack's parser.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-61772?
CVE-2025-61772 is a high-severity denial of service vulnerability in rack, published on 7 Oct 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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`).
Weakness: CWE-400
Which versions are affected by CVE-2025-61772?
6 open source packages ship an affected version, including rack. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
rack RubyGems | All versions | 2.2.19 |
rack RubyGems | All versions | 2.2.19 |
rack RubyGems | From 3.1 | 3.1.17 |
rack RubyGems | From 3.1 | 3.1.17 |
rack RubyGems | From 3.2 | 3.2.2 |
rack RubyGems | From 3.2 | 3.2.2 |
Products include Rack Rack.
How do I fix CVE-2025-61772?
Upgrade rack to a fixed version for your release line: 2.2.19, 3.1.17 or 3.2.2.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-61772 being exploited?
There is no known exploitation of CVE-2025-61772 in the wild and no public exploit code.
Other vulnerabilities in rack
- CVE-2026-34785 Rack: Local file inclusion in `Rack::Static` via URL Prefix Matching
- CVE-2026-34827 Rack: Algorithmic-Complexity DoS in Rack::Multipart::Parser
- CVE-2026-34829 Rack: Denial of Service via Unbounded Multipart File Upload Without Content-Length
- CVE-2026-22860 Rack has a Directory Traversal via Rack:Directory
- CVE-2025-61919 Rack is vulnerable to a memory-exhaustion DoS through unbounded URL-encoded body parsing
Sources
Also known as CLEANSTART-2026-UQ78689, CLEANSTART-2026-UU22048, DEBIAN-CVE-2025-61772, GHSA-wpv5-97wm-hp9c, MINI-3hrm-fcg3-jx3v, MINI-5qr9-4ff7-3787 and 13 more.