CVE-2025-69534: Python-Markdown Denial of Service Vulnerability Due to Unhandled AssertionError
Summary
CVE-2025-69534: Python-Markdown version 3.8 contain a vulnerability where malformed HTML-like sequences can cause html.parser.HTMLParser to raise an unhandled AssertionError during Markdown parsing. Affects markdown versions 1.7 – 3.9. No fix is published. How to fix ↓
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Background
Python-Markdown is a widely used library for converting Markdown text to HTML. It is designed to be simple and extensible, allowing developers to easily integrate Markdown processing into their applications. However, the library has a vulnerability that can lead to Denial of Service (DoS) when processing untrusted Markdown input, making it critical for applications that rely on user-generated content.
Vulnerability Detail
Python-Markdown version 3.8 contains a vulnerability where malformed HTML-like sequences can cause the html.parser.HTMLParser to raise an unhandled AssertionError during Markdown parsing. This issue arises because Python-Markdown does not catch this exception, leading to potential crashes in applications that process attacker-controlled Markdown. The ramifications include remote, unauthenticated Denial of Service in web applications, documentation systems, CI/CD pipelines, and any service that renders untrusted Markdown. The vulnerability can also lead to Information Disclosure through uncaught exceptions.
How To Fix
No fixed version is published for this vulnerability.
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Workaround
As a temporary workaround, you can implement input validation to sanitize Markdown content before processing it. This can help mitigate the risk of triggering the unhandled exception. For example, you can use a try-except block to catch potential exceptions during Markdown parsing:
try: html_output = markdown.markdown(user_input) except Exception as e: # Handle the exception, log it, or notify the user print('Error processing Markdown:', e)
Conclusion
The vulnerability identified as CVE-2025-69534 in Python-Markdown poses a significant risk of Denial of Service due to unhandled exceptions during Markdown parsing. It is crucial for developers to update to the patched version 3.8.1 or later and consider implementing input validation as a temporary workaround to mitigate risks.
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FAQ
The CVSS score of this vulnerability is 7.5, indicating a high severity level.
Python-Markdown versions prior to 3.8.1 are affected by this vulnerability.
You can use Vulert's playground at Vulert Scanner to check if your application is affected by this vulnerability without requiring any signup.
The potential impacts include Denial of Service in applications that process untrusted Markdown, which can disrupt service availability.
Yes, Vulert can monitor and alert you in real-time for open-source vulnerabilities in your software using just the Pipfile.lock.
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