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CVE-2026-34230

Rack: Quadratic complexity in Rack::Utils.select_best_encoding via wildcard Accept-Encoding header

Published: Apr 2, 2026Updated: Apr 16, 2026 Sources: CVE List NVD BDUCWE-400
NVD MITRE
5.3CVSSMEDIUM
EPSS Score
0.4%
Top 65.8%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:NI:NA:L
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:NIntegrity
None
A:LAvailability
Low
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Weaknesses

CWE-400CWE-407

Affected Products

rackrack
Library
OSS Libraries / web-framework
UbuntuCanonical Ltd.
On-premOS
Operating Systems / linux-distro
Red Hat Enterprise LinuxRed Hat Inc.
On-premOS
Operating Systems / linux-distro
Red Hat 3scale API Management PlatformRed Hat Inc.
SaaSSaaS Service
Cloud & SaaS / api-gateway
РЕД ОСООО «Ред Софт»
On-premOS
Operating Systems / linux-distro
rackoss-projectOSS Libraries
canonical ltd.commercialGBOperating Systemsaka canonical
red hat inc.commercialUSOperating Systemsaka red hat
ооо «ред софт»commercialRUOperating Systemsaka red soft
and 2 more affected products View all →

Attack Graph

Products CVE Techniques Tactics

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Exploitability

Official Patch Available

MITRE ATT&CK

1 technique
Impact
View detailed technique mapping

References

https://github.com/rack/rack/security/advisories/GHSA-v569-hp3g-36wr
github.com
https://github.com/rack/rack
github.com
https://github.com/rack/rack/security/advisories/GHSA-v569-hp3g-36wr
github.com
and 3 more references View all →

Timeline

Published
Apr 2, 2026
Last Updated
Apr 16, 2026

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