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MEDIUM severity

CVE-2009-4924 — python-cjson

MEDIUM

CVE-2009-4924 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in python-cjson. A fix is available for python-cjson — see the affected versions and patch details below.

Cross-site Scripting in python-cjson

Also known asPYSEC-2010-26
Published
Updated
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 ↗
1.4%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs71th percentile — riskier than 71% of all scored CVEsHighest risk
0.00%0.62%1.24%1.85%0.2%1.4%Apr 26Aug 26Oct 26

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

How urgent is this, really

CVE-2009-4924 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 < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected
🐍python-cjson

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Dan Pascu python-cjson 1.0.5 does not properly handle a ['/'] argument to cjson.encode, which makes it easier for remote attackers to conduct certain cross-site scripting (XSS) attacks involving Firefox and the end tag of a SCRIPT element.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIpython-cjsonall versions1.1.0pip install --upgrade 'python-cjson==1.1.0'

Affected Products

1 product · 1 configurations
Application
python-cjsondan_pascu
1 version
1.0.5

Detection & mitigation playbook

Open-source dependency

  1. Detect

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

  2. Fix

    Update python-cjson to 1.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2009-4924 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

Python-cjson 1.0.5 does not properly handle a ['/'] argument to cjson.encode, which makes it easier for remote attackers to conduct certain cross-site scripting (XSS) attacks involving Firefox and the end tag of a SCRIPT element.
O3 Security · Impact-Aware SCA

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CVE-2009-4924: python-cjson XSS — Fixed in 1.1.0