How severe is CVE-2026-33170?

No CVSS score has been assigned to CVE-2026-33170 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-33170?

CVE-2026-33170 affects the following packages: activesupport (RubyGems), activesupport (RubyGems), activesupport (RubyGems). Ecosystems affected: RubyGems.

How do I fix CVE-2026-33170?

Update activesupport to 8.1.2.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33170 is resolved across your whole dependency graph.

How do I detect CVE-2026-33170 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-2026-33170 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-2026-33170 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-33170 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-2026-33170?

CVE-2026-33170 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 28th 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-2026-33170?

CVE-2026-33170 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-2026-33170 published, and has it been updated?

CVE-2026-33170 was published on March 23, 2026 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

CVE-2026-33170 — activesupport

Fix: rails/rails@50d732a

CVE-2026-33170 is a Cross-site Scripting (XSS) vulnerability in activesupport. A fix is available for activesupport — see the affected versions and patch details below.

Rails Active Support has a possible XSS vulnerability in SafeBuffer#%

Also known asGHSA-89vf-4333-qx8v

Published

Mar 23, 2026

Updated

Oct 28, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Nov 7, 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-2026-33170.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs28th percentile — riskier than 28% of all scored CVEsHighest risk

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

Real-World Exposure

3 pkgs affected

💎activesupport💎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

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 possibly leading to XSS. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`activesupport`	≥ 8.1.0.beta1&&< 8.1.2.1	8.1.2.1`bundle update activesupport --conservative`
💎RubyGems	`activesupport`	≥ 8.0.0.beta1&&< 8.0.4.1	8.0.4.1`bundle update activesupport --conservative`
💎RubyGems	`activesupport`	all versions	7.2.3.1`bundle update activesupport --conservative`

Affected Products

1 product · 3 configurations

Application

railsrubyonrails

≥ 8.1.0 && < 8.1.2.1

range

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 8.1.2.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33170 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

This Cross-Site Scripting (XSS) flaw in Active Support bypasses ERB auto-escaping when a SafeBuffer is mutated in place and subsequently formatted with untrusted arguments. Applications like Red Hat Satellite using rubygem-activesupport are vulnerable only if they process user input using this exact mechanism. This…

Workaround published by Red Hat

Restrict Satellite HTTPS (443) access strictly to trusted administrative networks. On the Apache front-end, deploy a Web Application Firewall (WAF) to filter incoming XSS payloads, enforce a strict Content-Security-Policy (CSP) to block unauthorized inline script execution, and apply SameSite flags to session cookies

Source: Red Hat security advisory for CVE-2026-33170 (CC BY 4.0)

Frequently Asked Questions

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 possibly leading to XSS. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.

O3 Security · Impact-Aware SCA

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