CVE-2017-16876: mistune Cross-site scripting (XSS) vulnerability
Summary
CVE-2017-16876: mistune Cross-site scripting (XSS) vulnerability. Affects mistune versions < 0.8.1. Fixed in 0.8.1. How to fix ↓
Also tracked for
- mistune · Debian:11
The same CVE-2017-16876 is tracked separately for each ecosystem and vendor. Its fix information is the same; the package and affected versions differ.
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Background
Mistune is a Python package available on PyPI that provides a fast and full-featured Markdown parser. It is commonly used in web applications to parse and render Markdown content. The mistune package is vulnerable to a cross-site scripting (XSS) attack due to a failure to properly escape the 'key' argument in the _keyify function in mistune.py. This vulnerability allows remote attackers to inject arbitrary web script or HTML into the rendered output.
Vulnerability Detail
The mistune package before version 0.8.1 is affected by a cross-site scripting (XSS) vulnerability. The vulnerability originates from the _keyify function in mistune.py, which fails to properly escape the 'key' argument. This allows an attacker to inject malicious web script or HTML into the rendered output, potentially leading to the execution of arbitrary code or the theft of sensitive information. The impact of this vulnerability can range from defacement of web pages to the compromise of user accounts and the exfiltration of confidential data.
How To Fix
Latest published version: 3.4.0 as of 22 Oct 2026
pip install --upgrade "mistune==3.4.0"Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
0.8.1
This is the first release that contains the fix.
pip install --upgrade "mistune==0.8.1"Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
There is no known workaround for this vulnerability. It is essential to upgrade to the fixed version of mistune to mitigate the risk of XSS attacks.
Conclusion
The mistune package is vulnerable to a cross-site scripting (XSS) attack due to a failure to properly escape the 'key' argument in the _keyify function. To mitigate this vulnerability, it is essential to upgrade to mistune version 0.8.1 or later. This will ensure that the 'key' argument is properly escaped, preventing the injection of malicious web script or HTML. For further assistance or support in vulnerability remediation, please contact DevNack.com.
See every vulnerability recorded for mistune →
FAQ
Mistune is a Python package that provides a Markdown parser and renderer. It is commonly used in web applications to convert Markdown content into HTML.
Cross-site scripting (XSS) is a type of security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users. This can lead to the theft of sensitive information or the execution of arbitrary code.
The mistune XSS vulnerability is caused by a failure to properly escape the 'key' argument in the _keyify function. This allows an attacker to inject malicious web script or HTML into the rendered output, potentially leading to the execution of arbitrary code or the theft of sensitive information.
The impact of the mistune XSS vulnerability can range from defacement of web pages to the compromise of user accounts and the exfiltration of confidential data. Attackers can exploit this vulnerability to inject malicious scripts or HTML into the rendered output, affecting any user who views the affected content.
To protect your application from the mistune XSS vulnerability, it is crucial to upgrade to mistune version 0.8.1 or later. This version includes a fix for the XSS vulnerability. Additionally, it is recommended to regularly update your dependencies and follow secure coding practices to minimize the risk of XSS attacks.
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