CVE-2026-33170: Active Support is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework

Routine

MEDIUM 6.1UPGRADE

CVE-2026-33170 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.

Active Support is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework. Prior to versions 8.1.2.1, 8.0.4.1, and 7.2.3.1, `SafeBuffer#%` does not propagate the `@html_unsafe` flag to the newly created buffer. If a `SafeBuffer` is mutated in place (e.g. via `gsub!`) and then formatted with `%` using untrusted arguments, the result incorrectly reports `html_safe? == true`, bypassing ERB auto-escaping and possibl

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 73%)
CISA exploited list	No
Weakness	CWE-79
Published	2026-03-24
Last modified	2026-06-17

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

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-24 00:16 UTCPublished CVE record published
2026-06-17 10:37 UTCUpdated Record last modified

rubyonrails rails UPGRADE

Affected: < 7.2.3.1 · >= 8.0.0 and < 8.0.4.1 · >= 8.1.0 and < 8.1.2.1

Fixed in: 7.2.3.1, 8.0.4.1, 8.1.2.1

Safe to downgrade to: a release before 8.0.0

1. Check installed version

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

2. UPGRADE to 7.2.3.1 (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 8.0.0 (Debian / Ubuntu)

apt-cache madison rails sudo apt install rails=<VERSION_BEFORE_8.0.0> 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_8.0.0> 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-2026-33170?

rails: upgrade to 7.2.3.1, 8.0.4.1, 8.1.2.1. Exact commands for each OS are on this page.

Is CVE-2026-33170 being exploited?

CVE-2026-33170 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-2026-33170 affect?

CVE-2026-33170 affects rails. Severity is medium (CVSS 6.1). Active Support is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework. Prior to versions 8.1.2.1, 8.0.4.1, and 7.2.3.1, `SafeBuffer#%` does not propagate the `@html_unsafe` flag to the newly created bu

How urgent is CVE-2026-33170?

Priority 28/100. No elevated risk signals yet.

Software pages

Ruby on Rails vulnerabilities · Ruby vulnerabilities

Related CVEs

CVE-2023-22795 HIGH 7.5 UPGRADE MITIGATE A regular expression based DoS vulnerability in Action Dispatch <6.1.7.1 and <7.0.4.1 related to the If-None-M
CVE-2023-22792 HIGH 7.5 UPGRADE A regular expression based DoS vulnerability in Action Dispatch <6.0.6.1,< 6.1.7.1, and <7.0.4.1
CVE-2026-33167 MEDIUM 6.1 UPGRADE Action Pack is a Rubygem for building web applications on the Rails framework
CVE-2026-33195 CRITICAL 9.8 UPGRADE Active Storage allows users to attach cloud and local files in Rails applications
CVE-2026-33658 MEDIUM 6.5 UPGRADE Active Storage allows users to attach cloud and local files in Rails applications

References

← Back to latest CVEs