Is CVE-2026-34230 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-34230 being exploited in the wild.

How severe is CVE-2026-34230?

High severity, with a CVSS score of 7.5, published 2 April 2026.

Which products and versions are affected?

rack (RubyGems) ECOSYSTEM:introduced=0,fixed=2.2.23.

Is there a fix for CVE-2026-34230?

Yes. rack (RubyGems): upgrade to 2.2.23 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-34230 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-34230?

Check whether you run rack (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-34230: Rack inefficient algorithmic complexity in Rack::Utils.select_best_encoding

CVE-2026-34230 · Severity: high · CVSS 7.5 · Published 2026-04-02

Rack is a foundational software component used by many Ruby-based web applications to handle web requests. A flaw in how it processes certain web headers allows an unauthenticated attacker to send a specially crafted request that forces the server to consume excessive CPU resources. This can lead to a denial of service, making the web application slow or completely unresponsive to legitimate users.

Technologies: rack (RubyGems). Vendors: RubyGems.

Quick answers

Is CVE-2026-34230 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-34230 being exploited in the wild.
How severe is CVE-2026-34230?: High severity, with a CVSS score of 7.5, published 2 April 2026.
Which products and versions are affected?: rack (RubyGems) ECOSYSTEM:introduced=0,fixed=2.2.23.
Is there a fix for CVE-2026-34230?: Yes. rack (RubyGems): upgrade to 2.2.23 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-34230 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-34230?: Check whether you run rack (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

rack (RubyGems): upgrade to 2.2.23 or later
```
bundle update rack
```

Technical details

A denial of service vulnerability exists in Rack due to inefficient algorithmic complexity (CWE-407) in the `Rack::Utils.select_best_encoding` method. When processing the `Accept-Encoding` HTTP header, the method recomputes the set of available encodings for every wildcard (*) entry present in the header, resulting in quadratic time complexity. An unauthenticated remote attacker can exploit this by sending a single request with a large number of wildcard entries (e.g., 1,000 entries in an 8 KB header) to trigger disproportionate CPU consumption within the `Rack::Deflater` middleware. This issue is resolved in versions 2.2.23, 3.1.21, and 3.2.6.

Affected products

Rack Rack < 2.2.23, >= 3.0.0.beta1, < 3.1.21, >= 3.2.0, < 3.2.6

Identifiers

CVE-2026-34230
GHSA-v569-hp3g-36wr

Timeline

2026-04-01: advisory: GitHub Security Advisory published
2026-04-02: disclosed: NVD publication date

References

https://github.com/rack/rack/security/advisories/GHSA-v569-hp3g-36wr

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