Suspicious MSExchangeMailboxReplication ASPX Write

Severity: high
Author: Florian Roth (Nextron Systems)
Source: upstream

Detects suspicious activity in which the MSExchangeMailboxReplication process writes .asp and .apsx files to disk, which could be a sign of ProxyShell exploitation

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1190` Exploit Public-Facing Application
Persistence	`T1505.003` Server Software Component: Web Shell

Event coverage

Provider	Event ID	Title
Sysmon	11	FileCreate

Stages and Predicates

Stage 1: `selection`

or:
TargetFilename|endswith: .asp
TargetFilename|endswith: .aspx
Image|endswith: '\MSExchangeMailboxReplication.exe'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.