CVE-2025-61771 Rack's multipart parser buffers large non‑file fields entirely in memory, enabling DoS (memory exhaustion)
Attackers can cause denial of service by sending large non-file fields in multipart requests, exhausting memory in Rack applications.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-61771?
CVE-2025-61771 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` 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.
Weakness: CWE-400
Which versions are affected by CVE-2025-61771?
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-2025-61771?
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-2025-61771 being exploited?
There is no known exploitation of CVE-2025-61771 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-HZ91324, CLEANSTART-2026-VI91152, DEBIAN-CVE-2025-61771, GHSA-w9pc-fmgc-vxvw, MINI-382j-c87r-7rvc, MINI-592p-9jxp-2p74 and 13 more.