How severe is CVE-2023-28120?

CVE-2023-28120 has a CVSS score of 5.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2023-28120?

CVE-2023-28120 affects the following packages: activesupport (RubyGems), activesupport (RubyGems). Ecosystems affected: RubyGems.

How do I fix CVE-2023-28120?

Update activesupport to 7.0.4.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-28120 is resolved across your whole dependency graph.

How do I detect CVE-2023-28120 in my RubyGems dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for activesupport, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2023-28120 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2023-28120 actively exploited in the wild?

No public exploit code has been indexed for CVE-2023-28120 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2023-28120?

CVE-2023-28120 has an EPSS (Exploit Prediction Scoring System) score of 0.9%, placing it in the 61th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2023-28120?

CVE-2023-28120 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2023-28120 published, and has it been updated?

CVE-2023-28120 was published on January 9, 2025 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💎

💎 RubyGems

Not in CISA KEV

MEDIUM severity

CVE-2023-28120 — activesupport

MEDIUMFix: rails/rails@3cf23c3

CVE-2023-28120 is a medium-severity (CVSS 5.3) Cross-site Scripting (XSS) vulnerability in activesupport. A fix is available for activesupport — see the affected versions and patch details below.

Possible XSS Security Vulnerability in SafeBuffer#bytesplice

Also known asGHSA-pj73-v5mw-pm9j

Published

Jan 9, 2025

Updated

Oct 28, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2023-28120.

EPSS Exploitation Probability

via FIRST.org ↗

0.9%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs61th percentile — riskier than 61% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected

💎activesupport💎activesupport

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

There is a vulnerability in ActiveSupport if the new bytesplice method is called on a SafeBuffer with untrusted user input. This vulnerability has been assigned the CVE identifier CVE-2023-28120.

Versions Affected: All. Not affected: None Fixed Versions: 7.0.4.3, 6.1.7.3

Impact

ActiveSupport uses the SafeBuffer string subclass to tag strings as html_safe after they have been sanitized. When these strings are mutated, the tag is should be removed to mark them as no longer being html_safe.

Ruby 3.2 introduced a new bytesplice method which ActiveSupport did not yet understand to be a mutation. Users on older versions of Ruby are likely unaffected.

All users running an affected release and using bytesplice should either upgrade or use one of the workarounds immediately.

Workarounds

Avoid calling bytesplice on a SafeBuffer (html_safe) string with untrusted user input.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`activesupport`	≥ 7.0.0&&< 7.0.4.3	7.0.4.3`bundle update activesupport --conservative`
💎RubyGems	`activesupport`	all versions	6.1.7.3`bundle update activesupport --conservative`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for activesupport, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update activesupport to 7.0.4.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-28120 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Workaround published by Red Hat

Avoid calling bytesplice on a SafeBuffer (html_safe) string with untrusted user input.

Source: Red Hat security advisory for CVE-2023-28120 (CC BY 4.0)

Product	Fixed in	Advisory
RHOL-5.6-RHEL-8	`openshift-logging/fluentd-rhel8:v1.14.6-113`	RHSA-2023:1953
RHOL-5.7-RHEL-8	`openshift-logging/fluentd-rhel8:v1.14.6-140`	RHSA-2023:3495

Frequently Asked Questions

There is a vulnerability in ActiveSupport if the new bytesplice method is called on a SafeBuffer with untrusted user input. This vulnerability has been assigned the CVE identifier CVE-2023-28120. Versions Affected: All. Not affected: None Fixed Versions: 7.0.4.3, 6.1.7.3 # Impact ActiveSupport uses the SafeBuffer string subclass to tag strings as html_safe after they have been sanitized. When these strings are mutated, the tag is should be removed to mark them as no longer being html_safe. Ruby 3.2 introduced a new bytesplice method which ActiveSupport did not yet understand to be a mutati