CVE-2017-7796 in Firefox
Summary
by MITRE
On Windows systems, the logger run by the Windows updater deletes the file "update.log" before it runs in order to write a new log of that name. The path to this file is supplied at the command line to the updater and could be used in concert with another local exploit to delete a different file named "update.log" instead of the one intended. Note: This attack only affects Windows operating systems. Other operating systems are not affected. This vulnerability affects Firefox < 55.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 01/09/2021
The vulnerability identified as CVE-2017-7796 represents a critical file deletion flaw within the Windows update logging mechanism that operates with elevated privileges. This issue stems from the Windows updater service's improper handling of log file management where it attempts to delete the existing update.log file before creating a new one. The vulnerability manifests when command line arguments are used to specify the log file path, creating an opportunity for malicious actors to manipulate the file deletion process through local privilege escalation techniques. The flaw exists specifically within the Windows operating system environment and does not extend to other platforms, making it a Windows-specific security concern that affects the integrity of system logging processes.
The technical implementation of this vulnerability involves a race condition and path manipulation attack vector where an attacker can exploit the command line argument processing to redirect the file deletion operation to unintended targets. When the Windows updater processes command line parameters, it accepts the log file path without adequate validation or sanitization, allowing for path traversal or symbolic link manipulation. This creates a scenario where an attacker with local access can prepare a malicious file structure that causes the updater to delete a different file named update.log instead of the intended one. The vulnerability is classified under CWE-22 as improper limitation of a pathname to a restricted directory, and it aligns with ATT&CK technique T1059.001 for command and scripting interpreter. The flaw particularly affects Firefox versions prior to 55, indicating that web browser components may be leveraging this Windows system vulnerability through their update mechanisms.
The operational impact of CVE-2017-7796 extends beyond simple file deletion capabilities to potentially enable more sophisticated attacks within compromised Windows environments. An attacker exploiting this vulnerability could target critical system files, configuration data, or other sensitive files that happen to be named update.log in different directories, leading to system instability or complete compromise. The vulnerability's exploitation requires local system access but can be combined with other local exploits to achieve more significant damage through privilege escalation chains. This makes it particularly dangerous in environments where local access is possible through social engineering, compromised accounts, or other attack vectors. The vulnerability affects system integrity by allowing unauthorized deletion of log files that are crucial for security monitoring and incident response activities. Organizations with Windows systems running affected Firefox versions must consider this vulnerability as part of their broader security posture assessment, particularly in environments where system logs are critical for compliance and forensic analysis.
Mitigation strategies for CVE-2017-7796 should focus on immediate patching of Firefox to version 55 or later, which addresses the browser component of the vulnerability. System administrators should implement proper file system permissions and access controls to limit local user capabilities that could enable exploitation of this vulnerability. The Windows update process should be reviewed to ensure proper validation of command line arguments and implementation of secure file handling practices. Additionally, organizations should monitor for suspicious file deletion patterns in system logs and implement intrusion detection systems that can identify potential exploitation attempts. Regular security assessments should include verification that the Windows update process properly handles file paths without allowing path manipulation attacks, and network segmentation should be implemented to limit the potential impact of local privilege escalation attempts. The vulnerability highlights the importance of proper input validation and secure coding practices in system components that handle elevated privileges, particularly in update and maintenance processes that interact with the file system.