CVE-2026-34829: Rack is a modular Ruby web server interface

Routine

HIGH 7.5REMOTEUPGRADE

CVE-2026-34829 is a high-severity flaw (CVSS 7.5) 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::Multipart::Parser only wraps the request body in a BoundedIO when CONTENT_LENGTH is present. When a multipart/form-data request is sent without a Content-Length header, such as with HTTP chunked transfer encoding, multipart parsing continues until end-of-stream with no total size limit. For file parts, the uploaded body is written directly to a tempora

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 69%)
CISA exploited list	No
Weakness	CWE-400, CWE-770
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-2026-34829?

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

Is CVE-2026-34829 being exploited?

CVE-2026-34829 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-2026-34829 affect?

CVE-2026-34829 affects rack. Severity is high (CVSS 7.5). Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Multipart::Parser only wraps the request body in a BoundedIO when CONTENT_LENGTH is present. When a multipart/form-data request is sent without

How urgent is CVE-2026-34829?

Priority 39/100. High severity; 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
CVE-2026-34785 HIGH 7.5 UPGRADE Rack is a modular Ruby web server interface
CVE-2026-34230 MEDIUM 5.3 UPGRADE Rack is a modular Ruby web server interface
CVE-2026-34826 MEDIUM 5.3 UPGRADE Rack is a modular Ruby web server interface

References

← Back to latest CVEs