CVE-2021-30151 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in sidekiq. 1 public exploit reference exists, so weaponization risk is real. A fix is available for sidekiq — see the affected versions and patch details below.
Cross-site Scripting in Sidekiq
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-30151 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
sidekiq💎sidekiqReal-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
Sidekiq through 5.1.3 and 6.x through 6.2.0 allows XSS via the queue name of the live-poll feature when Internet Explorer is used.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | sidekiq | all versions | 5.2.0bundle update sidekiq --conservative |
| 💎RubyGems | sidekiq | ≥ 6.0.0&&< 6.2.1 | 6.2.1bundle update sidekiq --conservative |
Affected Products
sidekiqcontribsysdebian linuxdebianResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for sidekiq, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update sidekiq to 5.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-30151 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.
How to detect CVE-2021-30151
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2021-30151 -u https://target- Template
- Sidekiq <=6.2.0 - Cross-Site Scripting
- Severity
- medium
- Impact
- Successful exploitation of this vulnerability could lead to unauthorized access, data theft, or session hijacking.
- Remediation
- Upgrade to Sidekiq version 6.2.0 or later to mitigate this vulnerability.
Template by ProjectDiscovery nuclei-templates (DhiyaneshDk), MIT licensed. View the full template. Scan only systems you are authorised to test.
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 |
|---|---|---|
| Red Hat Satellite 6.11 for RHEL 7 | tfm-rubygem-sidekiq-0:5.2.10-1.el7sat | RHSA-2022:5498 |
Frequently Asked Questions
Is CVE-2021-30151 in your dependencies?
Find it across RubyGems, including transitive dependencies.