Full Report
On December 17, 2025 Cisco announced that they had detected a campaign exploiting a zero day in their email security devices. The vulnerability affects the physical and virtual versions of Cisco Secure Email Gateway, formerly known as Cisco Email Security Appliance (ESA), and ...
Analysis Summary
# Vulnerability: Zero-Day Exploitation in Cisco Secure Email Gateway (China-nexus Campaign)
## CVE Details
- CVE ID: CVE-2025-20393
- CVSS Score: *Score not provided in the source material* (Severity unknown)
- CWE: *CWE not provided in the source material*
## Affected Systems
- Products: Cisco Secure Email Gateway (formerly ESA), and Cisco Secure Email and Web Manager (formerly SMA).
- Versions: Physical and virtual versions are affected. Specific version numbers are not detailed.
- Configurations: The vulnerability requires the **Samp Quarantine feature** to be enabled and **reachable from the internet**.
## Vulnerability Description
The vulnerability allows for **Remote Code Execution (RCE)** on affected Cisco Secure Email devices. Successful exploitation is dependent on the Samp Quarantine feature being active and externally accessible.
## Exploitation
- Status: **Exploited in the wild** (By campaign UAT-9686).
- Complexity: *Complexity rating not provided in the source material*.
- Attack Vector: **Network** (Requires external reachability to the Samp Quarantine feature).
## Impact
- Confidentiality: High (Implied by remote code execution and deployment of data exfiltration/tunneling tools).
- Integrity: High (Implied by remote code execution and deployment of tools).
- Availability: Unknown (Exploitation leads to persistence, but direct availability impact is not specified).
## Remediation
### Patches
- **As of December 17, 2025, no patch or workaround is available.**
### Workarounds
- No official workarounds were provided at the time of the announcement.
* *Inference for mitigation (Not explicitly stated): Restricting external access to the Samp Quarantine feature may reduce exposure until a patch is released.*
## Detection
- Observed Post-Exploitation Techniques/Tools:
- **AquaShell:** Lightweight Python backdoor (passive command listening).
- **AquaPurge:** Utility used to delete log entries.
- **AquaTunnel:** ELF binary used to establish a reverse SSH connection.
- **Chisel:** Open-source tunneling tool used.
- Detection is centered around monitoring for anomalous processes, unexpected file creation (such as ELF binaries or Python scripts), and unexpected outbound network connections originating from the email security appliances, particularly reverse SSH or C2 traffic.
## References
- Vendor Advisories: Cisco official announcement (Date: December 17, 2025).
- Relevant Links: hxxps://blog.talosintelligence.com/uat-9686/