CVE-2018-10992 in LilyPond
Summary
by MITRE
lilypond-invoke-editor in LilyPond 2.19.80 does not validate strings before launching the program specified by the BROWSER environment variable, which allows remote attackers to conduct argument-injection attacks via a crafted URL, as demonstrated by a --proxy-pac-file argument, because the GNU Guile code uses the system Scheme procedure instead of the system* Scheme procedure. NOTE: this vulnerability exists because of an incomplete fix for CVE-2017-17523.
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Analysis
by VulDB Data Team • 02/04/2020
The vulnerability identified as CVE-2018-10992 affects LilyPond version 2.19.80 and specifically targets the lilypond-invoke-editor component. This issue represents a critical security flaw that stems from inadequate input validation within the software's handling of environment variables. The vulnerability is particularly concerning because it allows remote attackers to execute arbitrary commands on affected systems through a carefully crafted URL injection attack. The flaw manifests when the application processes strings before launching programs specified by the BROWSER environment variable, creating a pathway for malicious input to be interpreted as command-line arguments rather than benign data. This represents a classic command injection vulnerability that can be exploited across network boundaries without requiring local system access.
The technical implementation of this vulnerability lies in the GNU Guile scripting environment used by LilyPond, where the system Scheme procedure is employed instead of the more secure system* Scheme procedure. The system procedure does not properly sanitize input arguments, allowing attackers to inject additional command-line parameters that can be executed with the privileges of the user running LilyPond. When a malicious URL containing crafted arguments such as --proxy-pac-file is processed, these arguments are passed directly to the system call without proper validation or escaping. This behavior creates a scenario where attacker-controlled input can modify the execution context of external programs, potentially leading to arbitrary code execution. The vulnerability is particularly dangerous because it leverages the BROWSER environment variable, which is commonly used by applications to open web content, making it a legitimate attack vector that bypasses typical security controls.
The operational impact of this vulnerability extends beyond simple command execution, as it can enable attackers to perform a wide range of malicious activities including data exfiltration, privilege escalation, and system compromise. Remote attackers can exploit this vulnerability from any location without requiring physical access to the target system, making it particularly dangerous in enterprise environments where LilyPond might be used in automated workflows or shared computing environments. The vulnerability's persistence is further exacerbated by the fact that it represents an incomplete fix for CVE-2017-17523, indicating that security remediation efforts were not comprehensive enough to fully address the underlying input validation issues. This suggests a pattern of security oversights in the software's handling of environment variables and external command execution, which could potentially affect other components of the application. The vulnerability's exploitation can result in complete system compromise, particularly when LilyPond is run with elevated privileges or in environments where attackers can influence the BROWSER environment variable through various attack vectors.
Security mitigations for this vulnerability should focus on implementing proper input validation and sanitization mechanisms within the GNU Guile code. The most effective immediate fix involves replacing the system procedure with system* procedure throughout the lilypond-invoke-editor component, ensuring that all external command invocations properly escape or validate input parameters. Organizations should also implement environment variable restrictions, particularly for BROWSER, to prevent arbitrary URL handling from external sources. Network-level controls such as firewall rules and web application firewalls can help mitigate exploitation attempts by blocking suspicious URL patterns or limiting access to vulnerable systems. Additionally, system administrators should consider implementing least privilege principles when running LilyPond applications, reducing the potential impact of successful exploitation. The vulnerability aligns with CWE-78 which specifically addresses improper neutralization of special elements used in OS commands, and maps to ATT&CK technique T1059.001 for command and scripting interpreter, highlighting the need for comprehensive input validation and secure coding practices. Regular security audits and code reviews focusing on environment variable handling and external command execution should be implemented to prevent similar vulnerabilities from emerging in future releases.