Malicious Winter Vivern C2 Endpoint saveMessage via Proxy (via proxy)
- Category
- proxy
- Author
- HuntRule
- Published
- 2026-09-24
- Updated
- 2026-09-24
ATT&CK techniques
C2Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
Exfiltration
Impact
What it detects
This rule detects outbound HTTP requests to the /controlserver/saveMessage endpoint, the command-and-control path used by Winter Vivern after exploiting the CVE-2023-5631 Roundcube Webmail zero-day. Traffic to this endpoint indicates exfiltration of stolen webmail data to the group's C2 server.
Reporting behind it
Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.
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