Potential Modification of Accessibility Binaries

## Triage and analysis

### Investigating Potential Modification of Accessibility Binaries

Adversaries may establish persistence and/or elevate privileges by executing malicious content triggered by
accessibility features. Windows contains accessibility features that may be launched with a key combination before a
user has logged in (ex: when the user is on the Windows logon screen). An adversary can modify the way these programs
are launched to get a command prompt or backdoor without logging in to the system.

More details can be found [here](https://attack.mitre.org/techniques/T1546/008/).

This rule looks for the execution of supposed accessibility binaries that don't match any of the accessibility features
binaries' original file names, which is likely a custom binary deployed by the attacker.

#### Possible investigation steps

- Investigate the process execution chain (parent process tree).
- Identify the user account that performed the action and whether it should perform this kind of action.
- Contact the account owner and confirm whether they are aware of this activity.
- Investigate other alerts associated with the user/host during the past 48 hours.
- Check for similar behavior in other hosts on the environment.
- Retrieve the file and determine if it is malicious:
  - Use a private sandboxed malware analysis system to perform analysis.
    - Observe and collect information about the following activities:
      - Attempts to contact external domains and addresses.
      - File and registry access, modification, and creation activities.
      - Service creation and launch activities.
      - Scheduled tasks creation.
  - Use the PowerShell Get-FileHash cmdlet to get the SHA-256 hash value of the file.
    - Search for the existence and reputation of this file in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.

### False positive analysis

- This activity should not happen legitimately. The security team should address any potential benign true positive
(B-TP), as this configuration can put the user and the domain at risk.

### Response and remediation

- Initiate the incident response process based on the outcome of the triage.
- Isolate the involved host to prevent further post-compromise behavior.
- If the triage identified malware, search the environment for additional compromised hosts.
  - Implement any temporary network rules, procedures, and segmentation required to contain the malware.
  - Immediately block the IoCs identified.
- Remove and block malicious artifacts identified on the triage.
- Reset passwords for the user account and other potentially compromised accounts (email, services, CRMs, etc.).


## Config

If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define `event.ingested` and default fallback for EQL rules was not added until 8.2, so you will need to add a custom pipeline to populate `event.ingested` to @timestamp for this rule to work.