CVE-2026-4519 in CPython
Summary
by MITRE • 03/20/2026
The webbrowser.open() API would accept leading dashes in the URL which could be handled as command line options for certain web browsers. New behavior rejects leading dashes. Users are recommended to sanitize URLs prior to passing to webbrowser.open().
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 04/24/2026
The vulnerability identified as CVE-2026-4519 represents a command injection risk within the webbrowser.open() API implementation that could potentially allow attackers to execute arbitrary commands on affected systems. This flaw arises from the API's insufficient validation of input parameters, specifically its acceptance of URLs beginning with leading dashes that are typically reserved for command line options in various web browser implementations. The technical nature of this vulnerability aligns with CWE-77, which describes command injection flaws where untrusted data is incorporated into command line arguments without proper sanitization or validation. The issue demonstrates a classic input validation weakness where the API fails to properly distinguish between legitimate URL characters and potentially malicious command line indicators.
The operational impact of this vulnerability extends beyond simple browser functionality as it could enable attackers to manipulate web browser processes through carefully crafted URLs that contain leading dashes. When browsers encounter such URLs, they may interpret these leading dashes as command line flags or options, potentially triggering unintended behavior or even executing system commands if the browser process is not properly sandboxed. This type of vulnerability falls under the ATT&CK framework's technique T1059.007 for command and scripting interpreter, specifically targeting the execution of commands through legitimate system interfaces. The risk is particularly concerning in environments where applications utilize the webbrowser.open() API without proper URL sanitization, as it could provide attackers with a means to bypass traditional security controls that focus on web-based threats rather than command line injection vectors.
The remediation approach for CVE-2026-4519 centers on implementing robust input validation and sanitization practices within applications that utilize the webbrowser.open() API. Security practitioners should enforce strict URL validation that rejects or strips leading dashes from URLs before processing, ensuring that only valid web addresses are passed to browser execution functions. This approach aligns with defensive programming principles and follows the principle of least privilege by preventing potentially malicious input from reaching system-level processes. The recommended mitigation strategy also includes implementing proper URL encoding and validation libraries that can automatically detect and neutralize suspicious input patterns, particularly those containing special characters that could be interpreted as command line options. Organizations should also consider updating their application security testing procedures to include validation of API inputs for command injection vulnerabilities, ensuring that such issues are identified and addressed during the development lifecycle rather than after deployment. The vulnerability's resolution requires developers to adopt a proactive stance toward input sanitization, particularly when dealing with system-level APIs that interface directly with operating system components.