Rack's multipart byte range processing allows denial of service via excessive overlapping ranges

Exploitation

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

CVSS

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

EPSS

• CVE-2026-34826: 0.40% estimated exploitation activity in the next 30 days; percentile 33.78 (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::Utils.getbyteranges parses the HTTP Range header without limiting the number of individual byte ranges. Although the existing fix for CVE-2024-26141 rejects ranges whose total byte coverage exceeds the file size, it does not restrict the count of ranges. An attacker can supply many small overlapping ranges such as 0-0,0-0,0-0,... to trigger disproportionate CPU, memory, I/O, and bandwidth consumption per request. This results in a denial of service condition in Rack file-serving paths that process multipart byte range responses. Details Rack::Utils.getbyteranges accepts a comma-separated list of byte ranges and validates them based on their aggregate size, but does not impose a limit on how many individual ranges may be supplied. As a result, a request such as: can contain thousands of overlapping one-byte ranges while still satisfying the total-size check added for CVE-2024-26141. When such a header is processed by Rack’s file-serving code, each range causes additional…

Published by the source

2 Apr 2026, 19:07 UTC

Last modified by the source

13 May 2026, 15:21 UTC

Source last checked

26 Oct 2026, 15:51 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-x8cg-fq8g-mxfx

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# Patch Next advisory brief: CVE-2026-34826

Advisory: Rack's multipart byte range processing allows denial of service via excessive overlapping ranges
IDs: CVE-2026-34826, GHSA-x8cg-fq8g-mxfx
Record: https://patchnext.com/advisories/cve-2026-34826 (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: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: rack 3.2.6, 3.1.21, 2.2.23. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems rack: affected < 2.2.23; >= 3.0.0.beta1, < 3.1.21; >= 3.2.0, < 3.2.6; fixed in 3.1.21, 2.2.23, 3.2.6

## 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-x8cg-fq8g-mxfx (GitHub-reviewed advisory GHSA-x8cg-fq8g-mxfx lists affected ranges: RubyGems rack >=0 =3.0.0.beta1 =3.2.0 <3.2.6)

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