CVE-2017-17513 in TeX Live
Summary
by MITRE
TeX Live through 20170524 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, related to texmf-dist/scripts/context/stubs/mswin/mtxrun.lua and texmf-dist/tex/luatex/lualibs/lualibs-os.lua.
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Analysis
by VulDB Data Team • 12/15/2019
This vulnerability exists in TeX Live versions through 20170524 where the system fails to properly validate strings before executing programs specified in the BROWSER environment variable. The flaw manifests in two primary script files located within the TeX Live distribution: texmf-dist/scripts/context/stubs/mswin/mtxrun.lua and texmf-dist/tex/luatex/lualibs/lualibs-os.lua. These scripts handle browser invocation for documentation and help system functionality, creating a potential attack surface where malicious input could be executed with the privileges of the user running the TeX Live system.
The technical implementation of this vulnerability stems from improper input validation within the Lua script execution environment. When TeX Live attempts to launch a web browser for documentation viewing, it directly incorporates the BROWSER environment variable into system commands without sanitizing or validating the input. This creates a classic command injection vulnerability where remote attackers can craft malicious URLs that, when processed by these scripts, result in arbitrary command execution. The flaw is particularly dangerous because it operates at the system command level, potentially allowing attackers to execute arbitrary code on the target system with the privileges of the TeX Live user.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with a potential pathway for privilege escalation and system compromise. Since TeX Live installations often run with elevated privileges, especially in shared or server environments, successful exploitation could allow attackers to gain unauthorized access to system resources, modify or delete files, and potentially establish persistent access. The vulnerability affects systems where TeX Live is used for documentation viewing, particularly in environments where users might encounter malformed or malicious documentation links that trigger the vulnerable code paths. This makes the vulnerability particularly dangerous in collaborative environments or automated documentation generation systems.
Mitigation strategies for this vulnerability should focus on input validation and environment variable sanitization. System administrators should immediately upgrade to TeX Live versions released after 20170524 where the issue has been addressed through proper string validation. Organizations should also implement strict environment variable controls and consider using secure coding practices that validate all external inputs before processing. The vulnerability aligns with CWE-78, which describes improper neutralization of special elements used in OS commands, and relates to ATT&CK technique T1059.007 for command and scripting interpreter. Additionally, implementing principle of least privilege for TeX Live installations and monitoring for suspicious command execution patterns can help detect potential exploitation attempts. Regular security audits of script-based systems and proper input sanitization practices should be enforced to prevent similar vulnerabilities from emerging in other software components.