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MEDIUM severity

Cross-site scripting in actionpackGHSA-35mm-cc6r-8fjp

MEDIUM

GHSA-35mm-cc6r-8fjp is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in actionpack. 1 public exploit reference exists, so weaponization risk is real. A fix is available for actionpack — see the affected versions and patch details below.

Also known asCVE-2020-8264
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
1 known
Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
67.0%probability of exploitation in next 30 days
High Risk0.00%
Lower risk than most CVEs99th percentile — riskier than 99% of all scored CVEsHighest risk
0.00%30.6%61.2%91.8%0.3%67.0%Apr 26Aug 26Oct 26

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

How urgent is this, really

GHSA-35mm-cc6r-8fjp by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected
💎actionpack

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

In actionpack gem >= 6.0.0, a possible XSS vulnerability exists when an application is running in development mode allowing an attacker to send or embed (in another page) a specially crafted URL which can allow the attacker to execute JavaScript in the context of the local application. This vulnerability is in the Actionable Exceptions middleware.

Workarounds

Until such time as the patch can be applied, application developers should disable the Actionable Exceptions middleware in their development environment via a line such as this one in their config/environment/development.rb: config.middleware.delete ActionDispatch::ActionableExceptions

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
💎RubyGemsactionpack≥ 6.0.0&&< 6.0.3.46.0.3.4bundle update actionpack --conservative

Affected Products

1 product · 1 configurations
Application
railsrubyonrails
≥ 6.0.0 && < 6.0.3.4
range
Exploits & PoCs
1

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

In actionpack gem >= 6.0.0, a possible XSS vulnerability exists when an …

hackerone.comNVDJan 2021

Detection & mitigation playbook

Open-source dependency

  1. Detect

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

  2. Fix

    Update actionpack to 6.0.3.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-35mm-cc6r-8fjp is resolved across your whole dependency graph.

  3. 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.

Frequently Asked Questions

In actionpack gem >= 6.0.0, a possible XSS vulnerability exists when an application is running in development mode allowing an attacker to send or embed (in another page) a specially crafted URL which can allow the attacker to execute JavaScript in the context of the local application. This vulnerability is in the Actionable Exceptions middleware. Workarounds ----------- Until such time as the patch can be applied, application developers should disable the Actionable Exceptions middleware in their development environment via a line such as this one in their config/environment/development.rb:
O3 Security · Impact-Aware SCA

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Cross-site scripting in actionpack (Medium 6.1)