### Web Shell Deployment Analysis

Following the initial access via CVE-2021-26855, our systems have detected the deployment of a web shell, a common tactic for establishing persistence. This activity suggests the adversary is setting up a mechanism to maintain access to the compromised Exchange server.

#### Key Findings:
- **Location**: The web shell was deployed in the `/owa/auth` directory, a known vector for Hafnium operations.
- **File Signature**: The web shell file is obfuscated, consistent with previously observed Hafnium tactics.
- **Time of Deployment**: Occurred shortly after the initial access, indicating a pre-scripted procedure.

#### Recommendations:
- Conduct a thorough file system analysis to identify and remove unauthorized files.
- Implement additional monitoring on the affected server for unusual activity.

The next phase of the attack may involve attempts to move laterally within the network, leveraging the established persistence.