CVE-2006-1892 in Avast!
Summary
by MITRE
avast! 4 Linux Home Edition 1.0.5 allows local users to modify permissions of arbitrary files via a symlink attack on the /tmp/_avast4_ temporary directory.
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Analysis
by VulDB Data Team • 04/21/2018
The vulnerability described in CVE-2006-1892 represents a classic symlink attack scenario affecting avast! 4 Linux Home Edition version 1.0.5. This flaw enables local attackers to manipulate file permissions through a carefully crafted symbolic link attack against the temporary directory structure used by the antivirus software. The issue stems from improper handling of temporary file creation processes within the antivirus application's execution environment.
The technical exploitation of this vulnerability occurs through a race condition or insecure temporary file creation mechanism. When avast! creates temporary files in the /tmp/avast4 directory, it does not properly validate or secure the temporary file paths against symbolic link manipulation. An attacker can create a symbolic link with the same name as a file that the antivirus application expects to create, thereby redirecting the application's file operations to arbitrary locations on the filesystem. This allows the attacker to modify permissions of files they would normally not have access to, effectively bypassing normal access controls.
The operational impact of this vulnerability extends beyond simple privilege escalation as it represents a fundamental flaw in the application's security model for temporary file handling. Local users can leverage this weakness to gain unauthorized access to system resources, potentially leading to further compromise of the system. The attack vector is particularly concerning because it operates within the context of a legitimate system utility, making detection more difficult. This type of vulnerability falls under the CWE-377: Insecure Temporary File category, which specifically addresses weaknesses in temporary file creation and management that can be exploited by attackers.
From an attacker's perspective, this vulnerability provides a pathway to manipulate system files and potentially escalate privileges within the local environment. The attack requires local system access but does not require network connectivity, making it particularly dangerous in environments where local access is not strictly controlled. The vulnerability demonstrates poor adherence to security best practices in temporary file management and represents a failure to implement proper file access controls during temporary file creation processes.
The recommended mitigations for this vulnerability include immediate patching of the avast! 4 Linux Home Edition software to address the symlink handling issue. System administrators should ensure that all antivirus and security software is updated to the latest versions that properly address temporary file creation vulnerabilities. Additionally, implementing proper file permissions and using secure temporary file creation methods such as mkstemp or similar secure functions can prevent this class of attacks. The mitigation strategy should also include monitoring for unauthorized symbolic link creation in temporary directories and implementing proper access controls to limit the impact of such vulnerabilities. This issue aligns with ATT&CK technique T1059.007 for privilege escalation through file permission manipulation and represents a failure to implement proper sandboxing or temporary file security controls that would prevent such attacks from succeeding.