CVE-2025-61771
Rack is a modular Ruby web server interface. In versions prior to 2.2.19, 3.1.17, and 3.2.2, ``Rack::Multipart::Parserstores non-file form fields (parts without afilename) entirely in memory as Ruby Stringobjects. 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., Nginxclient_max_body_size`) and validating and rejecting unusually large form fields at the application level.
| Software | From | Fixed in |
|---|---|---|
rack
|
- | 2.2.19 |
|
rack
|
3.1 | 3.1.17 |
|
rack
|
3.2 | 3.2.2 |
| rack / rack | - | 2.2.19 |
| rack / rack | 3.1.0 | 3.1.17 |
| rack / rack | 3.2.0 | 3.2.2 |
- https://github.com/rack/rack/commit/589127f4ac8b5cf11cf88fb0cd116ffed4d2181e
- https://github.com/rack/rack/commit/d869fed663b113b95a74ad53e1b5cae6ab31f29e
- https://github.com/rack/rack/commit/e08f78c656c9394d6737c022bde087e0f33336fd
- https://github.com/rack/rack/security/advisories/GHSA-w9pc-fmgc-vxvw
- https://github.com/rubysec/ruby-advisory-db/blob/master/gems/rack/CVE-2025-61771.yml
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A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
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