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CVE-2025-20393 is an insufficient input validation vulnerability in the Spam Quarantine feature of Cisco AsyncOS Software for Cisco Secure Email Gateway and Cisco Secure Email and Web Manager. An unauthenticated remote attacker can send a crafted HTTP request to execute arbitrary operating-system commands with root privileges. A reported exploit chain in AsyncOS 15.5.3 involves truncation of single-byte length fields in the End User Quarantine RPC protocol: the send_message() function packs attacker-controlled destination lengths using Python 2.6 struct.pack(), allowing an oversized length to wrap to zero. The receiving read_message() function then treats the destination as empty, reportedly bypassing destination-based authentication and allowing attacker-controlled data to reach unsafe cPickle.loads() deserialization. The vulnerability was exploited as a zero-day from at least late November 2025.
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No valid public exploits. Mallory filtered out 10 candidates as fakes, detection scripts, or README-only repos.
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262 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Previously exploited CVSS 10.0 vulnerability affecting Cisco Secure Email Gateway/AsyncOS, referenced as background to the newer incident. It was exploited as a zero-day beginning in November 2025 and patched in January 2026.
A CVSS 10.0 Cisco AsyncOS zero-day affecting Secure Email Gateway and Secure Email and Web Manager appliances when Spam Quarantine was enabled and internet-exposed. It was exploited in the wild by a campaign attributed with moderate confidence to UAT-9686; mitigations preceded a patch released roughly seven weeks later.
A previous Cisco Secure Email Gateway vulnerability mentioned as historical context because it was added to CISA's Known Exploited Vulnerabilities catalog. The article provides no technical description, patch information, or attribution for this flaw.
A previously exploited critical Cisco AsyncOS vulnerability used to compromise Cisco Secure Email Gateway appliances and install persistence mechanisms.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.