JupyterLab: XSS due to lack of sanitization of the action attribute of an html <form>

Vulnerability

JupyterLab, a user interface for Project Jupyter, does not properly sanitize the action attribute of HTML ` elements in notebook cells [1][2]. This oversight allows an attacker to craft a malicious .ipynb` file that, when opened, triggers form validation outside the form itself, leading to cross-site scripting (XSS) [1][2]. The vulnerability affects JupyterLab versions prior to the fix introduced in commit 504825938c0abfa2fb8ff8d529308830a5ae42ed [3].

Exploitation

An attacker can create a specially crafted notebook containing a Markdown cell with a ` element that has a malicious action` attribute [1]. By combining this with HTML elements that trigger form events, the attacker can execute arbitrary JavaScript code in the context of the JupyterLab session [1]. The exploit requires user action: the victim must open the malicious notebook in JupyterLab [2]. No additional authentication or network position beyond normal access to the notebook is needed [1].

Impact

Successful exploitation results in remote code execution (RCE) with the privileges of the JupyterLab user [1]. The attacker can execute arbitrary JavaScript, which can then be used to run Python code on the kernel, access files, or compromise the entire Jupyter environment [1]. This leads to full compromise of the user's session and potential data exfiltration [1].

Mitigation

JupyterLab patched this vulnerability by removing the action attribute from `` tags during sanitization, as seen in commit 504825938c0abfa2fb8ff8d529308830a5ae42ed [3]. Users should upgrade to a fixed version (e.g., 3.1.4 or later) [4]. There is no known workaround other than not opening untrusted notebooks. The CVE is not listed in CISA's Known Exploited Vulnerabilities catalog.