CVE-2023-28120 is a medium-severity (CVSS 5.3) vulnerability in activesupport. A fix is available for activesupport — see the affected versions and patch details below.
Possible XSS Security Vulnerability in SafeBuffer#bytesplice
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
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2023-28120 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
activesupport💎activesupportReal-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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | activesupport | ≥ 7.0.0&&< 7.0.4.3 | 7.0.4.3bundle update activesupport --conservative |
| 💎RubyGems | activesupport | all versions | 6.1.7.3bundle update activesupport --conservative |
Detection & mitigation playbook
Open-source dependencyDetect
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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2023-28120 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-28120. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
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.
| 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
Is CVE-2023-28120 in your dependencies?
O3 Security finds CVE-2023-28120 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.