T1573.001 Symmetric Cryptography Mappings

This is an authentication bypass vulnerability that can enable remote code execution. Numerous post-exploitation impacts by threat actors are detailed in the referenced CISA report.

CVE-2021-44077 is an unauthenticated remote code execution vulnerability. The following post-exploitation activity has been observed by adversaries: writing webshells to disk for persistence, obfuscating and deobfuscating/decoding files or information, dumping user credentials, only using signed windows binaries for follow-on actions, adding/deleting user accounts as needed, exfiltrating the active directory database, using windows management instrumentation for remote execution, deleting files to remove indicators from the host, discovering domain accounts, collecting and archiving files for exfiltration, and using symmetric encryption for command and control.

This vulnerability is exploited by an attacker who has obtained administrative console access on the target system. The vulnerability lies in the Win32k driver, specifically in the NtGdiResetDC function, due to improper handling of user-mode callbacks. This vulnerability has been exploited by threat actors to gain elevated privileges on Windows servers. Attackers leveraged this flaw to execute arbitrary kernel commands, allowing them to manipulate system processes and potentially deploy additional malware or perform further malicious activities. The exploit in question is actively being used in the wild, primarily in espionage campaigns. It involves triggering a use-after-free condition by executing the ResetDC function a second time for the same handle during a callback. Once the vulnerability is exploited, attackers can manipulate memory to perform arbitrary kernel function calls with controlled parameters. This allows them to achieve their objectives, such as reading and writing kernel memory, with the same permissions as the compromised system's user.