How severe is CVE-2026-34230?

CVE-2026-34230 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.

Is CVE-2026-34230 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-34230?

CVE-2026-34230 affects Rack. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-34230?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-34230 have an EU (EUVD) identifier?

Yes. CVE-2026-34230 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-18378.

When was CVE-2026-34230 published?

CVE-2026-34230 was published on 2026-04-02 and last updated on 2026-06-17.

CVE-2026-34230

CVE-2026-34230 is a medium-severity vulnerability in Rack with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-400.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
EPSS exploit prediction: 0% (35th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-18378
Weakness: CWE-400
Affected product: Rack
Published: 2026-04-02
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-34230?: 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.
How severe is CVE-2026-34230?: CVE-2026-34230 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
Is CVE-2026-34230 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-34230?: CVE-2026-34230 affects Rack. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-34230?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-34230 have an EU (EUVD) identifier?: Yes. CVE-2026-34230 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-18378.
When was CVE-2026-34230 published?: CVE-2026-34230 was published on 2026-04-02 and last updated on 2026-06-17.

References

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

Affected products (1)

cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*

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