Denial of Service Vulnerability in Rack by Rack Developers
CVE-2026-34230

5.3MEDIUM

Key Information:

Vendor

Rack

Status
Rack
Vendor
CVE Published:
2 April 2026

What is CVE-2026-34230?

A denial of service vulnerability has been identified in the Rack modular Ruby web server interface. Specifically, prior to the releases 2.2.23, 3.1.21, and 3.2.6, the method Rack::Utils.select_best_encoding exhibits a problematic quadratic time complexity when processing Accept-Encoding values with numerous wildcard entries. This vulnerability allows an unauthenticated attacker to exploit a single crafted request, leading to excessive CPU usage by the compression middleware, potentially rendering applications that use Rack::Deflater inoperable. Users are advised to upgrade to non-vulnerable versions to mitigate this issue.

Affected Version(s)

rack < 2.2.23 < 2.2.23

rack >= 3.0.0.beta1, < 3.1.21 < 3.0.0.beta1, 3.1.21

rack >= 3.2.0, < 3.2.6 < 3.2.0, 3.2.6

References

https://github.com/rack/rack/security/advisories/GHSA-v56...
x_refsource_CONFIRM

CVSS V3.1

Score:
5.3
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.