Vulnerabilities > CVE-2022-4149 - Time-of-check Time-of-use (TOCTOU) Race Condition vulnerability in Netskope
Summary
The Netskope client service (prior to R96) on Windows runs as NT AUTHORITY\SYSTEM which writes log files to a writable directory (C:\Users\Public\netSkope) for a standard user. The files are created and written with a SYSTEM account except one file (logplaceholder) which inherits permission giving all users full access control list. Netskope client restricts access to this file by allowing only read permissions as a standard user. Whenever the Netskope client service restarts, it deletes the logplaceholder and recreates, creating a race condition, which can be exploited by a malicious local user to create the file and set ACL permissions on the file. Once the file is created by a malicious user with proper ACL permissions, all files within C:\Users\Public\netSkope\ becomes modifiable by the unprivileged user. By using Windows pseudo-symlink, these files can be pointed to other places in the system and thus malicious users will be able to elevate privileges.
Vulnerable Configurations
| Part | Description | Count |
|---|---|---|
| Application | 8 | |
| OS | 1 |
Common Weakness Enumeration (CWE)
Common Attack Pattern Enumeration and Classification (CAPEC)
- Leveraging Race Conditions via Symbolic Links This attack leverages the use of symbolic links (Symlinks) in order to write to sensitive files. An attacker can create a Symlink link to a target file not otherwise accessible to her. When the privileged program tries to create a temporary file with the same name as the Symlink link, it will actually write to the target file pointed to by the attackers' Symlink link. If the attacker can insert malicious content in the temporary file she will be writing to the sensitive file by using the Symlink. The race occurs because the system checks if the temporary file exists, then creates the file. The attacker would typically create the Symlink during the interval between the check and the creation of the temporary file.
- Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions This attack targets a race condition occurring between the time of check (state) for a resource and the time of use of a resource. The typical example is the file access. The attacker can leverage a file access race condition by "running the race", meaning that he would modify the resource between the first time the target program accesses the file and the time the target program uses the file. During that period of time, the attacker could do something such as replace the file and cause an escalation of privilege.