Executive brief
Rack is a foundational software component used by many Ruby-based web applications to handle web requests. A vulnerability in how it processes file uploads allows an attacker to send an unlimited amount of data to the server, potentially filling up the server's storage space. This can lead to a denial-of-service (DoS) condition, causing the application to crash or become unavailable to legitimate users.
Technical details
A resource exhaustion vulnerability exists in Rack::Multipart::Parser. The parser only applies a BoundedIO wrapper to the request body when a Content-Length header is explicitly provided. If an attacker sends a multipart/form-data request using HTTP chunked transfer encoding (omitting Content-Length), the parser continues reading until the end-of-stream without a total size limit. While Rack normally enforces memory limits for non-file parts, file parts containing a filename are streamed directly to a temporary file on disk without being subject to these constraints. An unauthenticated remote attacker can exploit this to consume unbounded disk space, leading to a denial-of-service. This issue is patched in versions 2.2.23, 3.1.21, and 3.2.6.
Affected products
- Rack Rack < 2.2.23, >= 3.0.0.beta1 < 3.1.21, >= 3.2.0 < 3.2.6
- Red Hat Logging Subsystem for Red Hat OpenShift 5
- Red Hat Red Hat 3scale API Management Platform 2 2
Timeline
- 2026-04-01: advisory: GitHub Security Advisory published
- 2026-04-02: disclosed: NVD publication date