CVE-2026-34230
Rack: Quadratic complexity in Rack::Utils.select_best_encoding via wildcard Accept-Encoding header
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.
INFO
Published Date :
April 2, 2026, 5:16 p.m.
Last Modified :
April 16, 2026, 5:27 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 3.1 | HIGH | [email protected] |
Solution
- Update Rack to version 2.2.23 or later.
- Update Rack to version 3.1.21 or later.
- Update Rack to version 3.2.6 or later.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-34230.
| URL | Resource |
|---|---|
| https://github.com/rack/rack/security/advisories/GHSA-v569-hp3g-36wr | Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-34230 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-34230
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-34230 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-34230 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Apr. 16, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Added CPE Configuration OR *cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:* versions from (including) 3.0.0 up to (excluding) 3.1.21 *cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:* versions from (including) 3.2.0 up to (excluding) 3.2.6 *cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:* versions up to (excluding) 2.2.23 Added Reference Type GitHub, Inc.: https://github.com/rack/rack/security/advisories/GHSA-v569-hp3g-36wr Types: Vendor Advisory -
New CVE Received by [email protected]
Apr. 02, 2026
Action Type Old Value New Value Added 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Added CWE CWE-407 Added CWE CWE-400 Added Reference https://github.com/rack/rack/security/advisories/GHSA-v569-hp3g-36wr