![]() ![]() This is done for security reasons and therefore, we strongly recommend you do not use a blank password if you want to run scheduled tasks. Every scheduled task runs under a user login account that requires a valid user with password on the operating system.īy default, Windows OS does not allow users to schedule task when a blank password is used to login into the system. ![]() You can find me on Twitter at and follow the team for the latest in exploit techniques and security patches.Syncrify uses Windows built-in Task Scheduler to run backup tasks. Thanks also should go out to my colleagues at Trend Micro Research for their help in the analysis of this vulnerability. Given the publicity this has generated, and the high level of privilege held by the Task Scheduler service, it does seem safe to anticipate attacks sooner rather than later. Microsoft gave this bug an Exploit Index rating of 1, which means they believe attackers will start to use this vulnerability within 30 days. If successfully exploited, the attacker could take complete control of the target system. This analysis shows how a locally-authenticated attacker can leverage this vulnerability to write malicious code to critical system executables, and thereby escalate privilege to SYSTEM – even without knowing the password of a user. Therefore, this vulnerability is significantly more serious than has been recognized previously or publicly acknowledged. Testing confirms that this technique is perfectly valid. If not, this method will fail.Īccording to this, even a low-privileged client may pass in a NULL value in place of a password, provided that: (a) the specified flag is set, and (b) the caller is not attempting to create a task that runs as the local system account. If pwszAccountName specifies the local system account, the caller must be an administrator on the local computer or an application running in the local system account. Use the IScheduledWorkItem::SetFlags method to set the flag. If you set the TASK_FLAG_RUN_ONLY_IF_LOGGED_ON flag, you may also set pwszPassword to NULL for local or domain user accounts. Set this parameter to NULL if the local system account is specified. However, in the documentation for the Task Scheduler COM API, one finds the following information regarding the password parameter (pwszPassword) of the SetAccountInformation method: For example, if malware executes with user-level privileges, it may not know the cleartext password. ![]() This somewhat limits the usability of the exploit in a real-world attack scenario. The posted exploit code requires the attacker to possess the cleartext password of the account being used for the attack. Through this, an attacker can gain full control of any local file on all versions of Windows 10. Since this file is actually a hard link, this security information will be applied to the target file. The Task Scheduler service will update the security information on the file in the preferred folder, granting ownership and full control to the attacker. Use the Task Scheduler RPC interface to migrate the task to the preferred folder. Manually place a new task with the same name into the legacy folder. Replace the file in the preferred folder with a hard link to an arbitrary target file. The essential steps of the attack are as follows: This particular combination of behaviors leaves an opening for a hard link attack. One consequence of this is that a client can manually place a file in the legacy folder, then make use of the Task Scheduler to have the task migrated to the preferred folder. The permissions on the two task folders permit all authenticated users to create files within those folders. Critically, the Task Scheduler service performs this action using its own highly-privileged SYSTEM token. When saving a task file to the preferred location, the service will set security information on the file granting ownership and full control to the owner of the task. ![]()
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