How severe is CVE-2013-4939?

No CVSS score has been assigned to CVE-2013-4939 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2013-4939?

CVE-2013-4939 affects the following packages: yui (npm). Ecosystems affected: npm.

How do I fix CVE-2013-4939?

Update yui to 3.10.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2013-4939 is resolved across your whole dependency graph.

How do I detect CVE-2013-4939 in my npm dependencies?

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

How do I mitigate CVE-2013-4939 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-2013-4939 actively exploited in the wild?

No public exploit code has been indexed for CVE-2013-4939 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-2013-4939?

CVE-2013-4939 has an EPSS (Exploit Prediction Scoring System) score of 1.5%, placing it in the 73th 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-2013-4939?

CVE-2013-4939 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-2013-4939 published, and has it been updated?

CVE-2013-4939 was published on September 1, 2020 and was last updated on November 8, 2023. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2013-4939 — yui

CVE-2013-4939 is a Cross-site Scripting (XSS) vulnerability in yui. A fix is available for yui — see the affected versions and patch details below.

Cross-Site Scripting in yui

Published

Sep 1, 2020

Updated

Nov 8, 2023

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs73th percentile — riskier than 73% of all scored CVEsHighest risk

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

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

53other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

yuinpm

22Kdownloads / week

Description

Affected versions of yui are vulnerable to cross-site scripting in the uploader.swf and io.swf utilities, via script injection in the url.

Recommendation

YUI has published their recommendation to fix this issue. Their recommendation is to:

Delete self-hosted copies of these files if you are not using them
Use the Yahoo! CDN hosted files
Use the patched files provided on the YUI Library here.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`yui`	all versions	3.10.3`npm install yui@3.10.3`

Affected Products

2 products · 58 configurations

Application

moodlemoodle

36 versions

2.1.02.1.12.1.22.1.32.1.42.1.52.1.62.1.72.1.82.1.92.1.102.2.0

Application

yuiyahoo

22 versions

3.0.03.1.03.1.13.1.23.2.03.3.03.4.03.4.13.5.03.5.13.6.03.7.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for yui, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update yui to 3.10.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2013-4939 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.

Frequently Asked Questions

Affected versions of `yui` are vulnerable to cross-site scripting in the `uploader.swf` and `io.swf` utilities, via script injection in the url. ## Recommendation YUI has published their recommendation to fix this issue. Their recommendation is to: - Delete self-hosted copies of these files if you are not using them - Use the Yahoo! CDN hosted files - Use the patched files provided on the YUI Library [here](https://yuilibrary.com/support/20130515-vulnerability/#resolution).

O3 Security · Impact-Aware SCA

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