Rack is vulnerable to a memory-exhaustion DoS through unbounded URL-encoded body parsing

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2025-61919: 0.65% estimated exploitation activity in the next 30 days; percentile 51.12 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Details When handling non-multipart form submissions, Rack’s request parser performs: Since read is called with no argument, the entire request body is loaded into a Ruby String. This occurs before query parameter parsing or enforcement of any paramslimit. As a result, Rack applications without an upstream body-size limit can experience unbounded memory allocation proportional to request size. Impact Attackers can send large application/x-www-form-urlencoded bodies to consume process memory, causing slowdowns or termination by the operating system (OOM). The effect scales linearly with request size and concurrency. Even with parsing limits…

Published by the source

10 Oct 2025, 17:33 UTC

Last modified by the source

13 Oct 2025, 15:46 UTC

Source last checked

26 Oct 2026, 15:51 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-6xw4-3v39-52mm

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# Patch Next advisory brief: CVE-2025-61919

Advisory: Rack is vulnerable to a memory-exhaustion DoS through unbounded URL-encoded body parsing
IDs: CVE-2025-61919, GHSA-6xw4-3v39-52mm
Record: https://patchnext.com/advisories/cve-2025-61919 (revision 1, source checked 26 Oct 2026, 15:51 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: rack 3.2.3, 3.1.18, 2.2.20. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems rack: affected < 2.2.20; >= 3.0, < 3.1.18; >= 3.2, < 3.2.3; fixed in 3.1.18, 3.2.3, 2.2.20

## Suggested inspection (read-only)
- RubyGems rack: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on rack.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-6xw4-3v39-52mm (GitHub-reviewed advisory GHSA-6xw4-3v39-52mm lists affected ranges: RubyGems rack >=0 =3.0 =3.2 <3.2.3)

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