Review reviewHigh

CVE-2026-34230

rack

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Utils.select_best_encoding processes Accept-Encoding values with quadratic time complexity when the header contains many wildcard (*) entries. Because this method is used by Rack::Deflater to choose a response encoding, an unauthenticated attacker can send a single request with a crafted Accept-Encoding header and cause disproportionate CPU consumption on the compression middleware path. This results in a denial of service condition for applications using Rack::Deflater. This issue has been patch...

CVSS: 7.5
EPSS: 0.43%
CISA KEV: Not listed
Published: 2026.04.03

PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV

Exploit probability0.43%

Technical severityCVSS 7.5

Vulnerability overview

Affected product and versions

Product: rack
Affected versions: >= < 2.2.23, >= >= 3.0.0.beta1, < 3.1.21, >= >= 3.2.0, < 3.2.6, < 2.2.23, >= 3.0.0 < 3.1.21, >= 3.2.0 < 3.2.6
Fixed versions: 2.2.23, 3.1.21, 3.2.6

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide

1
Identify
Confirm that rack and an affected version are present.
2
Prioritize
Combine exploitation signals with asset exposure and business criticality.
3
Remediate
Follow the vendor advisory or supported update path and preserve rollback options.
4
Verify
Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE: CWE-400, CWE-407