Description
Rack is a modular Ruby web server interface. Prior to versions 2.2.20, 3.1.18, and 3.2.3, `Rack::Request#POST` reads the entire request body into memory for `Content-Type: application/x-www-form-urlencoded`, calling `rack.input.read(nil)` without enforcing a length or cap. Large request bodies can therefore be buffered completely into process memory before parsing, leading to denial of service (DoS) through memory exhaustion. Users should upgrade to Rack version 2.2.20, 3.1.18, or 3.2.3, anu of which enforces form parameter limits using `query_parser.bytesize_limit`, preventing unbounded reads of `application/x-www-form-urlencoded` bodies. Additionally, enforce strict maximum body size at the proxy or web server layer (e.g., Nginx `client_max_body_size`, Apache `LimitRequestBody`).
Affected products
rack: rack
References4
- github.com/rack/rack/commit/4e2c903991a790ee211a3021808ff4fd6fe… Patch
- github.com/rack/rack/commit/cbd541e8a3d0c5830a3c9a30d3718ce2e12… Patch
- github.com/rack/rack/commit/e179614c4a653283286f5f046428cbb85f2… Patch
- github.com/rack/rack/security/advisories/GHSA-6xw4-3v39-52mm MitigationThird Party Advisory
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - EPSS — exploit probability
- 1% percentile: 51 · as of 9 November 2026
- CWE
- CWE-400
Could this be exploited in your environment?
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