CVE-2009-5079 in groff
Summary
by MITRE
The (1) gendef.sh, (2) doc/fixinfo.sh, and (3) contrib/gdiffmk/tests/runtests.in scripts in GNU troff (aka groff) 1.21 and earlier allow local users to overwrite arbitrary files via a symlink attack on a gro#####.tmp or /tmp/##### temporary file.
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Analysis
by VulDB Data Team • 02/09/2019
The vulnerability identified as CVE-2009-5079 affects GNU troff version 1.21 and earlier, specifically targeting three critical shell scripts: gendef.sh, doc/fixinfo.sh, and contrib/gdiffmk/tests/runtests.in. This represents a classic symlink attack or race condition vulnerability that exploits improper temporary file handling in Unix-like systems. The flaw occurs when these scripts create temporary files using predictable naming patterns such as gro#####.tmp or /tmp/#####, making them susceptible to symbolic link attacks where malicious users can manipulate the file system to redirect file operations to arbitrary locations.
The technical implementation of this vulnerability stems from the insecure creation of temporary files without proper atomic operations or validation of file existence. When these scripts execute and attempt to write to temporary files, they do not verify whether the target file is a symbolic link or if it already exists. This allows local attackers to pre-create symbolic links in the temporary directory with names matching those used by the scripts, effectively causing the scripts to write data to files chosen by the attacker rather than the intended temporary locations. The vulnerability aligns with CWE-377, which addresses insecure temporary file creation practices, and demonstrates a failure to implement proper file system security controls.
The operational impact of this vulnerability is significant for systems running affected versions of GNU troff, as it enables local privilege escalation and arbitrary file overwrite capabilities. Attackers can leverage this vulnerability to modify critical system files, inject malicious code into configuration files, or overwrite binaries that the scripts might be processing. The attack vector is particularly dangerous because it requires minimal privileges and can be executed by any local user, making it a preferred target for privilege escalation attacks. This vulnerability also relates to ATT&CK technique T1059.007 for Unix Shell and T1068 for Local Privilege Escalation, as it provides a mechanism for attackers to gain elevated system access through script-based exploitation.
Mitigation strategies for CVE-2009-5079 should focus on immediate patching of affected GNU troff installations to versions 1.22 or later, where the temporary file handling has been corrected. System administrators should also implement proper file system permissions and consider using secure temporary file creation methods such as mkstemp() or similar atomic operations that guarantee file uniqueness and prevent symlink attacks. Additional defensive measures include monitoring for unauthorized symbolic link creation in temporary directories, implementing proper file system integrity checks, and ensuring that scripts do not run with elevated privileges when processing temporary files. The vulnerability highlights the importance of following secure coding practices and the principle of least privilege in script development, particularly when dealing with temporary file operations in multi-user environments. Organizations should also conduct comprehensive vulnerability assessments to identify similar insecure temporary file usage patterns in other system components and ensure that all software installations are kept current with security patches.