CVE-2021-41134 : Exploit Details and Defense Strategies

nbdime provides tools for diffing and merging of Jupyter Notebooks. In affected versions a stored cross-site scripting (XSS) issue exists within the Jupyter-owned nbdime project. The vulnerability allows an attacker to execute malicious scripts in a user's browser, potentially compromising sensitive data.

Understanding CVE-2021-41134

What is CVE-2021-41134?

A stored Cross-Site Scripting (XSS) vulnerability was discovered in nbdime, a tool used for comparing and managing Jupyter Notebooks. The issue arises from improper handling of input during the rendering of HTML content, allowing malicious scripts to be injected.

The Impact of CVE-2021-41134

The vulnerability has a CVSS base score of 8.7, indicating a high severity level. It affects confidentiality, integrity, and requires low privileges to exploit. Attackers can exploit this flaw to execute arbitrary script code in the context of the user's session, leading to potential data theft or compromise.

Technical Details of CVE-2021-41134

Vulnerability Description

The stored XSS issue in nbdime occurs when processing the file name and path of Jupyter Notebooks. The extension fails to sanitize the constructed string before displaying it, leading to script injection. Specifically, the diffNotebookCheckpoint function is vulnerable, allowing for the execution of malicious scripts.

Affected Systems and Versions

nbdime < 1.1.1 (pip)
nbdime >= 2.0.0, < 2.1.1 (pip)
nbdime >= 3.0.0, < 3.1.1 (pip)
nbdime < 5.0.2 (npm)
nbdime >= 6.0.0, < 6.1.2 (npm)
nbdime-jupyterlab < 1.0.1 (npm)
nbdime-jupyterlab >= 2.0.0, < 2.1.1 (npm)

Exploitation Mechanism

The vulnerability is exploited by luring a victim to open a crafted Jupyter Notebook or diff operation that triggers the improper rendering of HTML content. This can lead to the execution of malicious scripts in the context of the user's session, enabling various attacks.

Mitigation and Prevention

Immediate Steps to Take

Update nbdime to the latest patched version immediately
Avoid opening untrusted Jupyter Notebooks or running diff operations on untrusted content

Long-Term Security Practices

Regularly update software dependencies to mitigate known vulnerabilities
Educate users on safe handling of Jupyter Notebooks and caution against opening files from unknown or untrusted sources

Patching and Updates

Apply patches released by the vendor promptly to address the XSS vulnerability and ensure system security.