CVE-2017-17517 in Sylpheed
Summary
by MITRE
libsylph/utils.c in Sylpheed through 3.6 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 • 12/15/2019
The vulnerability identified as CVE-2017-17517 resides within the Sylpheed email client version 3.6 and earlier, specifically in the libsylph/utils.c file where improper string validation occurs before executing programs referenced by the BROWSER environment variable. This flaw represents a classic command injection vulnerability that can be exploited by remote attackers to manipulate the execution flow of the application. The issue stems from the application's failure to sanitize user-supplied input when constructing command-line arguments for external program execution, creating an avenue for malicious code injection through crafted URLs.
This vulnerability operates under the CWE-78 principle of improper neutralization of special elements used in OS commands, specifically manifesting as an argument injection attack vector. When Sylpheed processes URLs that contain specially crafted payloads, the application fails to properly validate or escape the input before incorporating it into shell commands that reference the BROWSER environment variable. The ATT&CK framework categorizes this as a command injection technique under the T1059.003 sub-technique, where adversaries exploit weak input validation to inject malicious commands that execute within the victim's environment. The flaw is particularly dangerous because it allows remote attackers to execute arbitrary commands with the privileges of the user running Sylpheed, potentially leading to complete system compromise.
The operational impact of this vulnerability extends beyond simple command execution, as it enables attackers to perform a wide range of malicious activities including but not limited to arbitrary code execution, privilege escalation, data exfiltration, and system reconnaissance. An attacker could craft a malicious URL that, when clicked within Sylpheed, would cause the application to execute unintended shell commands through the BROWSER environment variable. This could result in the installation of backdoors, modification of system files, or unauthorized access to sensitive information. The vulnerability is particularly concerning in environments where users may encounter untrusted email content, as it requires no special privileges beyond the ability to send email messages containing malicious URLs.
Mitigation strategies for CVE-2017-17517 should focus on input validation and proper sanitization of all external inputs before command execution. The most effective immediate fix involves implementing strict validation and escaping of strings before incorporating them into shell commands, ensuring that special characters are properly neutralized. System administrators should also consider implementing environment variable restrictions and using secure coding practices that avoid direct shell command construction from user inputs. Additionally, deploying network-level protections such as web application firewalls and email filtering systems can help detect and block malicious URLs before they reach vulnerable systems. The vulnerability highlights the critical importance of following secure coding guidelines and implementing proper input validation mechanisms to prevent injection attacks. Organizations should also consider upgrading to patched versions of Sylpheed or migrating to more modern email clients that have addressed similar vulnerabilities. Regular security audits and penetration testing should be conducted to identify and remediate similar issues in other applications that may be susceptible to command injection attacks through environment variable manipulation.