AquaShell
AquaShell is a custom lightweight Python backdoor used for persistence on compromised Cisco AsyncOS appliances, particularly Cisco Secure Email Gateway (SEG) and Cisco Secure Email and Web Manager (SEWM/SMA) systems targeted in exploitation of CVE-2025-20393. Cisco Talos attributed the related activity with moderate confidence to the China-nexus threat actor UAT-9686. The malware is described as a passive listener/backdoor embedded into Cisco AsyncOS web components, including a modified index.py or other web server file, and installed by decoding an encoded data blob. It receives encoded, including base64-encoded, commands via unauthenticated HTTP POST requests and executes them in the system shell, enabling covert arbitrary command execution and system-level access. Reported post-compromise activity shows AquaShell deployed alongside AquaTunnel/ReverseSSH and Chisel for reverse tunneling and traffic proxying, and AquaPurge for log clearing and anti-forensics. The campaign affected a limited subset of appliances with non-standard configurations, especially where the Spam Quarantine feature was enabled and exposed to the internet. High-confidence indicators mentioned in the content include the malware name/string "AquaShell" itself and its presence as a hallmark post-compromise tool in this Cisco AsyncOS intrusion set.
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Vulnerabilities exploited
1 CVE Mallory has correlated with this family across public research and vendor advisories. Each row links to the full Mallory page for that vulnerability.
The campaign is exploiting an unpatched zero-day vulnerability... It allows threat actors to execute arbitrary commands with root privileges on affected devices... Recommendations for CVE-2025-20393
Groups observed using it
1 distinct threat actor attributed by public researchers. Open in Mallory to see the full evidence chain and overlapping campaigns.
Techniques & procedures
1 distinct technique documented for this family, organized by ATT&CK tactic.
Persistence
1 techniqueStealth
1 techniqueRecent activity
30 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Lightweight Python backdoor that accepts encoded commands via unauthenticated HTTP POST and executes them in the system shell; linked by Talos to UAT-9686.
Lightweight Python backdoor used post-exploitation to receive and execute base64-encoded commands, enabling flexible C2 on compromised Cisco email security appliances.
Custom-made Python backdoor installed on compromised Cisco Email Security appliances to provide attacker access/persistence.
A custom persistence/backdoor mechanism deployed post-exploitation to maintain long-term access on compromised Cisco Secure Email appliances.
The version that knows your environment.
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Named campaigns wielding this family, with evidence pinned to each claim.
CVEs this family uses for access and lateral movement.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Every documented technique, ranked by evidence weight.
Reddit, Mastodon, and CTI community discussion around this family.