Vulnerability · Published Apr 2, 2026 · Assigned by GitHub_M
CVE-2026-34230Rack: Quadratic complexity in Rack::Utils.select_best_encoding via wildcard Accept-Encoding header
Medium 5.3
In plain English
A medium-severity uncontrolled resource consumption in rack from rack. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 39% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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 patched in versions 2.2.23, 3.1.21, and 3.2.6.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | ruby-rack | 2.2.22-0+deb12u2 | DEBIAN-CVE-2026-34230 |
| Debian:13 | ruby-rack | 3.1.20-0+deb13u2 | DEBIAN-CVE-2026-34230 |
| Debian:14 | ruby-rack | 3.2.6-2 | DEBIAN-CVE-2026-34230 |
| RubyGems | rack | 2.2.23 | GHSA-v569-hp3g-36wr |
| RubyGems | rack | 3.1.21 | GHSA-v569-hp3g-36wr |
| RubyGems | rack | 3.2.6 | GHSA-v569-hp3g-36wr |
| Ubuntu:24.04:LTS | ruby-rack | 2.2.7-1ubuntu0.7 | UBUNTU-CVE-2026-34230 |
| Ubuntu:25.10 | ruby-rack | 3.1.16-0.1ubuntu0.3 | UBUNTU-CVE-2026-34230 |
| Ubuntu:26.04:LTS | ruby-rack | 3.2.4-1ubuntu1.1 | UBUNTU-CVE-2026-34230 |
| Ubuntu:26.04:LTS | ruby-rack | 3.2.4-1ubuntu1.1 | USN-8989-1 |
Affected products (as reported)
Weakness: CWE-400, CWE-407 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
References
- https://github.com/rack/rack/security/advisories/GHSA-v569-hp3g-36wr x_refsource_CONFIRM