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Cisco has confirmed that a serious zero-day vulnerability allowing remote code execution is being actively exploited in its Secure Email Gateway and Secure Email and Web Manager appliances.
The CVE-2025-20393 flaw lets unauthorized attackers run arbitrary root commands by sending specific HTTP requests to the Spam Quarantine feature. Cisco aware of the attacks on December 10, 2025, with signs of exploitation beginning in November 2025.
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Exploitation Campaign and Threat Actor:
Cisco Talos believes the campaign is linked to UAT-9686, a China-based advanced threat group, with moderate confidence due to similarities with APT41 and UNC5174.
Attackers use a Python backdoor named AquaShell for ongoing remote access, along with tools like AquaTunnel and Chisel for internal movement, and AquaPurge to clear logs and avoid detection. Their main targets are telecommunications and critical infrastructure, emphasizing espionage over ransomware.
Mitigation and Fixed Releases:
Cisco Secure Email Gateway Fixed Releases
| Vulnerable Release | First Fixed Release |
|---|---|
| 14.2 and earlier | 15.0.5-016 |
| 15.0 | 15.0.5-016 |
| 15.5 | 15.5.4-012 |
| 16.0 | 16.0.4-016 |
Cisco Secure Email and Web Manager Fixed Releases
| Vulnerable Release | First Fixed Release |
|---|---|
| 15.0 and earlier | 15.0.2-007 |
| 15.5 | 15.5.4-007 |
| 16.0 | 16.0.4-010 |
Cisco released patches to fix the vulnerability and eliminate known persistence methods; there are no workarounds. Administrators must upgrade immediately and check Spam Quarantine status in the web interface under Network > IP Interfaces.
