Rack: Multipart parser buffers large non‑file fields entirely in memory, enabling DoS (memory exhaustion)

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-2025-61771: 0.56% estimated exploitation activity in the next 30 days; percentile 46.71 (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::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). Details During multipart parsing, file parts are streamed to temporary files, but non-file parts are buffered into memory: There is no size limit on these in-memory buffers. As a result, any large text field—while technically valid—will be loaded fully into process memory before being added to params. Impact 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. Mitigation Upgrade: Use a patched version of Rack that enforces a…

Published by the source

7 Oct 2025, 17:27 UTC

Last modified by the source

13 Oct 2025, 15:29 UTC

Source last checked

26 Oct 2026, 15:51 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-w9pc-fmgc-vxvw

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# Patch Next advisory brief: CVE-2025-61771

Advisory: Rack: Multipart parser buffers large non‑file fields entirely in memory, enabling DoS (memory exhaustion)
IDs: CVE-2025-61771, GHSA-w9pc-fmgc-vxvw
Record: https://patchnext.com/advisories/cve-2025-61771 (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 3.2.2, 3.1.17, 2.2.19. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems rack: affected < 2.2.19; >= 3.1, < 3.1.17; >= 3.2, < 3.2.2; fixed in 3.2.2, 2.2.19, 3.1.17

## 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-w9pc-fmgc-vxvw (GitHub-reviewed advisory GHSA-w9pc-fmgc-vxvw lists affected ranges: RubyGems rack >=0 =3.1 =3.2 <3.2.2)

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