CVE-2026-33167: Action Pack is a Rubygem for building web applications on the Rails framework

Routine

MEDIUM 6.1UPGRADE

CVE-2026-33167 is a medium-severity flaw (CVSS 6.1) affecting rails. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Action Pack is a Rubygem for building web applications on the Rails framework. In versions on the 8.1 branch prior to 8.1.2.1, the debug exceptions page does not properly escape exception messages. A carefully crafted exception message could inject arbitrary HTML and JavaScript into the page, leading to XSS. This affects applications with detailed exception pages enabled (`config.consider_all_requests_local = true`), which is the default in devel

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.3% (top 82%)
CISA exploited list	No
Weakness	CWE-79
Published	2026-03-23
Last modified	2026-08-12

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

Last updated 2026-08-12 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-23 23:17 UTCPublished CVE record published
2026-08-12 16:45 UTCUpdated Record last modified

rubyonrails rails UPGRADE

Affected: >= 8.1.0 and < 8.1.2.1

Fixed in: 8.1.2.1

Safe to downgrade to: a release before 8.1.0

1. Check installed version

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

2. UPGRADE to 8.1.2.1 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade rails

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 8.1.0 (Debian / Ubuntu)

apt-cache madison rails sudo apt install rails=<VERSION_BEFORE_8.1.0> sudo apt-mark hold rails

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

dnf --showduplicates list rails sudo dnf downgrade rails-<VERSION_BEFORE_8.1.0> sudo dnf versionlock add rails

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-2026-33167?

rails: upgrade to 8.1.2.1. Exact commands for each OS are on this page.

Is CVE-2026-33167 being exploited?

CVE-2026-33167 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-2026-33167 affect?

CVE-2026-33167 affects rails. Severity is medium (CVSS 6.1). Action Pack is a Rubygem for building web applications on the Rails framework. In versions on the 8.1 branch prior to 8.1.2.1, the debug exceptions page does not properly escape exception messages. A carefully crafted exception message coul

How urgent is CVE-2026-33167?

Priority 26/100. No elevated risk signals yet.

Software pages

Ruby on Rails vulnerabilities

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References

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