CVE-2017-17524 in SWI-Prolog
Summary
by MITRE
library/www_browser.pl in SWI-Prolog 7.2.3 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.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 12/15/2019
The vulnerability identified as CVE-2017-17524 resides within the SWI-Prolog software version 7.2.3, specifically in the library/www_browser.pl component that handles web browser launching functionality. This flaw represents a classic command injection vulnerability that occurs when user-provided input is not properly sanitized before being used in system commands. The issue manifests when SWI-Prolog attempts to launch an external web browser by referencing the BROWSER environment variable, creating a pathway for malicious actors to inject arbitrary commands through crafted URL inputs. The vulnerability falls under the category of improper input validation, which is systematically categorized as CWE-20 by the Common Weakness Enumeration framework.
The technical exploitation of this vulnerability occurs when SWI-Prolog processes web requests and subsequently calls the system command using the BROWSER environment variable without adequate sanitization of the URL parameter. Attackers can craft malicious URLs that contain shell metacharacters or command injection sequences, which then get interpreted by the underlying shell when the browser launching command executes. This creates a remote code execution vector where an attacker could potentially execute arbitrary commands with the privileges of the SWI-Prolog process. The attack surface is particularly concerning in environments where SWI-Prolog is deployed as a web service or integrated into web applications, as it allows for remote exploitation without requiring authentication.
The operational impact of this vulnerability extends beyond simple command injection, as it can enable attackers to escalate privileges, access sensitive system resources, or compromise the entire hosting environment. In web-based applications, this vulnerability can be leveraged to gain unauthorized access to server files, execute malicious payloads, or establish persistent backdoors. The vulnerability's remote nature means that attackers can exploit it from anywhere on the internet, making it particularly dangerous for publicly accessible SWI-Prolog installations. According to the MITRE ATT&CK framework, this vulnerability maps to techniques involving command injection and privilege escalation, with potential lateral movement capabilities once initial access is achieved.
Mitigation strategies for CVE-2017-17524 should focus on implementing proper input validation and sanitization of all user-supplied data before it is processed by system commands. Organizations should immediately upgrade to SWI-Prolog versions that have patched this vulnerability, as the maintainers have addressed the issue in subsequent releases. Additionally, system administrators should implement environment variable restrictions and consider using secure coding practices that prevent shell command injection by using safer alternatives such as direct API calls instead of shell invocation. The implementation of proper access controls and network segmentation can also limit the potential impact of exploitation. Security monitoring should include detection of unusual command execution patterns and unauthorized modifications to environment variables. Organizations should also consider implementing web application firewalls and input validation mechanisms that can detect and block malicious URL patterns before they reach the vulnerable component. The vulnerability highlights the importance of following secure coding practices and proper input sanitization, particularly when dealing with system-level operations that involve user-provided data.