CVE-2026-34230: Rack is a modular Ruby web server interface

Routine

MEDIUM 5.3REMOTEUPGRADE

CVE-2026-34230 is a medium-severity flaw (CVSS 5.3) affecting rack. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 63%)
CISA exploited list	No
Weakness	CWE-400, CWE-407
Published	2026-04-02
Last modified	2026-07-24

Publisher (CNA): GitHub, Inc. · Vendor: rack

Last updated 2026-07-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-02 17:16 UTCPublished CVE record published
2026-07-24 21:10 UTCUpdated Record last modified

rack rack UPGRADE

Affected: < 2.2.23 · >= 3.0.0 and < 3.1.21 · >= 3.2.0 and < 3.2.6

Fixed in: 2.2.23, 3.1.21, 3.2.6

Safe to downgrade to: a release before 3.0.0

1. Check installed version

apt-cache policy rack || rpm -q rack || rack --version

2. UPGRADE to 2.2.23 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade rack

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade rack

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 3.0.0 (Debian / Ubuntu)

apt-cache madison rack sudo apt install rack=<VERSION_BEFORE_3.0.0> sudo apt-mark hold rack

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list rack sudo dnf downgrade rack-<VERSION_BEFORE_3.0.0> sudo dnf versionlock add rack

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-34230?

rack: upgrade to 2.2.23, 3.1.21, 3.2.6. Exact commands for each OS are on this page.

Is CVE-2026-34230 being exploited?

CVE-2026-34230 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-34230 affect?

CVE-2026-34230 affects rack. Severity is medium (CVSS 5.3). 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. B

How urgent is CVE-2026-34230?

Priority 33/100. Remotely exploitable, no login, no user action

Software pages

Ruby vulnerabilities

Related CVEs

CVE-2023-27530 HIGH 7.5 UPGRADE MITIGATE A DoS vulnerability exists in Rack <v3.0.4.2, <v2.2.6.3, <v2.1.4.3 and <v2.0.9.3 within in the Multipart MIME
CVE-2026-34827 HIGH 7.5 UPGRADE Rack is a modular Ruby web server interface
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References

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