CVE-2017-17522 in Python
Summary
by MITRE
Lib/webbrowser.py in Python through 3.6.3 does not validate strings before launching the program specified by the BROWSER environment variable, which might allow remote attackers to conduct argument-injection attacks via a crafted URL.
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Analysis
by VulDB Data Team • 08/06/2024
The vulnerability identified as CVE-2017-17522 resides within Python's standard library implementation in the lib/webbrowser.py module, affecting Python versions through 3.6.3. This flaw represents a critical security oversight that enables remote attackers to execute arbitrary commands through argument injection techniques. The vulnerability specifically manifests when the webbrowser module processes URLs that contain maliciously crafted arguments, as it fails to properly sanitize or validate input strings before invoking external programs specified by the BROWSER environment variable. This design flaw creates a dangerous attack vector where malicious actors can manipulate the execution flow of the webbrowser module by crafting specially formatted URLs that contain command injection payloads.
The technical mechanism behind this vulnerability stems from the lack of proper input validation and sanitization within the webbrowser module's handling of environment variables. When applications call functions within the webbrowser module to open URLs, the module retrieves the BROWSER environment variable and attempts to execute the specified program without performing adequate validation of the URL string. This behavior creates an argument injection scenario where attacker-controlled input can be interpreted as command-line arguments by the underlying browser executable. The vulnerability is classified under CWE-77 and CWE-94, representing command injection and code injection weaknesses respectively, as it allows attackers to inject and execute arbitrary commands through the browser launching mechanism. The ATT&CK framework categorizes this under T1059.001 for command and scripting interpreter, specifically targeting the execution of commands through legitimate system utilities.
The operational impact of CVE-2017-17522 extends beyond simple privilege escalation as it can enable attackers to execute arbitrary code on vulnerable systems with the privileges of the user running the Python application. This vulnerability is particularly concerning because it can be exploited remotely without requiring any special privileges or authentication, making it an attractive target for automated attacks. Attackers can craft malicious URLs that, when processed by vulnerable Python applications, will execute unintended commands on the target system. The vulnerability affects any Python application that relies on the standard webbrowser module for URL handling, including web applications, network tools, and automated scripts that may process user-provided URLs. This widespread applicability makes the vulnerability particularly dangerous in enterprise environments where Python applications are commonly deployed.
Mitigation strategies for CVE-2017-17522 involve several approaches that address the root cause of the vulnerability. The primary and most effective solution is to upgrade to Python versions 3.6.4 or later, where the vulnerability has been resolved through proper input validation and sanitization mechanisms. Organizations should also implement strict environment variable controls by validating and sanitizing the BROWSER environment variable before application execution, ensuring that it only contains legitimate browser paths. Additionally, application developers should avoid using the webbrowser module with untrusted input and implement proper input validation at all levels of their applications. Network-level protections can include firewall rules that restrict access to potentially vulnerable Python applications and monitoring for suspicious URL patterns that may indicate exploitation attempts. The vulnerability highlights the importance of proper input validation and the principle of least privilege in software development, emphasizing that standard library components should not introduce security risks when processing untrusted data.