# CVE-2026-9769: JustHTML uncontrolled recursion DoS via deeply nested HTML

Source: https://junglewise.ai/threats/cve-2026-9769-justhtml-uncontrolled-recursion-dos-via-deeply-nested-html  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-23. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-9769 · Severity: high · CVSS 7.5 · Published 2026-08-23

JustHTML is a Python HTML parsing library used to sanitize and process HTML content. An attacker can craft malicious HTML with deeply nested tags to trigger a crash during parsing. Depending on how an application handles exceptions, this could cause request failures, service interruption, or worker process termination—effectively a denial-of-service attack.

Technologies: [justhtml (PyPI)](https://junglewise.ai/threats/technologies/justhtml). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-9769 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-9769 being exploited in the wild.

**How severe is CVE-2026-9769?** High severity, with a CVSS score of 7.5, published 23 August 2026.

**Which products and versions are affected?** justhtml (PyPI) <= 1.9.1, ECOSYSTEM:introduced=0,fixed=1.10.0.

**Is there a fix for CVE-2026-9769?** Yes. justhtml (PyPI): upgrade to 1.10.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-9769 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-9769?** Check whether you run justhtml (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- justhtml (PyPI): upgrade to 1.10.0 or later

  ```sh
  pip install "justhtml>=1.10.0"
  ```


## Technical details

The vulnerability is an uncontrolled recursion flaw (CWE-674) in the JustHTML DOM tree traversal functions. The root cause is in _find_elements() (and related functions like _node_to_html(), clone_node(deep=True), and _to_markdown_walk()), which recursively walk the DOM tree without enforcing a depth limit. When JustHTML.__init__() parses HTML, it unconditionally calls TreeBuilder.finish() → _populate_selectedcontent() → _find_elements(), which recursively traverses all nodes. On CPython with the default recursion limit of 1000, approximately 11 KB of nested &lt;div&gt; tags triggers RecursionError. No authentication or special privileges are required; any attacker who can supply HTML input (via web form, API, file upload, etc.) can trigger the error. The attack vector is network-based with low complexity. The library already demonstrates the correct pattern using iterative traversal in comparable functions, and a fix is available in version 1.10.0 by converting recursive implementations to iterative stack-based traversal.

## Affected products

- Emil Stenstrom JustHTML <= 1.9.1

## Identifiers

- CVE-2026-9769
- GHSA-v7cf-c9rm-wm3j
- PYSEC-2026-3854

## Timeline

- 2026-03-17: disclosed: Published to GitHub Advisory Database
- 2026-03-15: patched: Fixed in version 1.10.0

## References

- [https://api.github.com/users/kq5y](https://api.github.com/users/kq5y)
- [https://github.com/kq5y](https://github.com/kq5y)
- [https://api.github.com/users/kq5y/gists%7B/gist_id%7D](https://api.github.com/users/kq5y/gists%7B/gist_id%7D)
- [https://api.github.com/users/kq5y/repos](https://api.github.com/users/kq5y/repos)
- [https://avatars.githubusercontent.com/u/46104508?v=4](https://avatars.githubusercontent.com/u/46104508?v=4)
- [https://api.github.com/users/kq5y/events%7B/privacy%7D](https://api.github.com/users/kq5y/events%7B/privacy%7D)

## Related threats

- [justhtml uncontrolled recursion DoS via deeply nested HTML](https://junglewise.ai/threats/justhtml-uncontrolled-recursion-dos-via-deeply-nested-html-26591bb6)
- [justhtml mutation XSS in raw-text element serialization](https://junglewise.ai/threats/cve-2026-8630-justhtml-mutation-xss-in-raw-text-element-serialization)
- [justhtml HTML escaping bypass in Markdown conversion](https://junglewise.ai/threats/cve-2026-8445-justhtml-html-escaping-bypass-in-markdown-conversion)
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- [justhtml to_markdown() cross-site scripting in code span](https://junglewise.ai/threats/cve-2026-77088-justhtml-to-markdown-cross-site-scripting-in-code-span)