Researchers have identified four vulnerabilities in Windows task scheduling, posing significant risks of privilege escalation and log tampering. The issues reside in “schtasks.exe,” a binary that allows administrators to manage scheduled tasks on both local and remote computers. One critical vulnerability is a User Account Control (UAC) bypass, which allows attackers to execute high-privilege commands without user approval, potentially compromising system security. By exploiting this, attackers can escalate privileges and run malicious payloads with administrative rights.
The vulnerability occurs when an attacker creates a scheduled task using a password instead of an interactive token, granting them maximum privileges. To exploit this flaw, the attacker must obtain the password through various means, such as cracking an NTLMv2 hash. This could occur after exploiting flaws like CVE-2023-21726, allowing a low-privileged user to impersonate a member of groups like Administrators or Backup Operators.
With this access, attackers can execute commands that could lead to unauthorized access or data theft.
In addition to privilege escalation, attackers can use this vulnerability to erase activity logs, making it harder to detect malicious actions. This is accomplished by registering a task using a long author name in an XML file, which overwrites the Task Event Log. Additionally, security logs, such as “Security.evtx,” can be overwritten, erasing evidence of prior activities. These actions enable attackers to cover their tracks by deleting audit trails of their exploits.
This set of vulnerabilities highlights the risks associated with the Windows Task Scheduler, a component accessible to users with sufficient knowledge.
Cybersecurity researchers emphasize that these flaws enable attackers to impersonate any user and gain elevated privileges, bypassing security controls. Organizations should be aware of these issues and take steps to mitigate the risk by applying patches and monitoring for suspicious activities.
