CVE-2006-1231 in CAPI4HylaFAX
Summary
by MITRE
CAPI4HylaFAX 1.3, when compiled with GENERATE_DEBUGSFFDATAFILE set, allows local users to modify arbitrary files via a symlink attack on the c2faxrecv_dbgdatafile.sff temporary file.
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Analysis
by VulDB Data Team • 07/21/2018
The vulnerability identified as CVE-2006-1231 resides within CAPI4HylaFAX version 1.3, a telecommunications software package designed for fax transmission and reception over ISDN lines. This flaw manifests when the software is compiled with the GENERATE_DEBUGSFFDATAFILE flag enabled, creating a dangerous condition that exposes the system to privilege escalation through symbolic link manipulation. The issue fundamentally stems from inadequate temporary file handling practices during the debugging process, creating a window of opportunity for malicious local users to exploit the system's trust in temporary file creation.
The technical mechanism behind this vulnerability involves the creation of a temporary file named c2faxrecv_dbgdatafile.sff, which is generated during the debugging process of the fax reception functionality. When the software operates with elevated privileges during debugging, it creates this temporary file without proper validation of the file system state. A local attacker can exploit this by creating a symbolic link with the same name in the directory where the temporary file is expected to be created, effectively redirecting the debug data to a location of their choosing. This symlink attack allows the attacker to write arbitrary data to files that they would normally not have permission to modify, effectively bypassing normal file system access controls and privilege boundaries.
The operational impact of this vulnerability extends beyond simple file modification capabilities, representing a significant security risk for systems running CAPI4HylaFAX with debugging enabled. Local users who can execute the software with sufficient privileges to trigger the debug functionality can escalate their access to modify critical system files, configuration data, or even inject malicious code into the system. This represents a classic privilege escalation vulnerability that can be leveraged to establish persistent access or cause system instability through the modification of core system components. The vulnerability is particularly concerning in multi-user environments where local access might be more readily available than anticipated.
Mitigation strategies for this vulnerability must address both the immediate technical flaw and the broader security practices surrounding software compilation and execution. The primary recommendation involves disabling the GENERATE_DEBUGSFFDATAFILE flag during production deployments, as this eliminates the vulnerable code path entirely. Additionally, system administrators should implement proper file system permissions and ensure that temporary file creation occurs in secure directories with appropriate access controls. The vulnerability aligns with CWE-354, which specifically addresses the weakness of inadequate verification of security properties during debugging, and can be mapped to ATT&CK technique T1068, which covers the exploitation of privilege escalation vulnerabilities through local attack vectors. Organizations should also consider implementing mandatory access controls and monitoring for unusual file system activities that might indicate symlink attacks or unauthorized file modifications.