CVE-2026-20242: Deserialization of Untrusted Data
Source GCVE Database
Not known to be exploited · CVSS 9.8 Critical.
Data as of 31 Oct 2026, 20:20 UTC
- EPSS
- 0.8% chance of exploitation in 30 days – higher than 59% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 16 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 31 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| CiscoCisco Secure Firewall Management Center (FMC) | Affected
| Fixed in– |
AI-suggested
Mitigation includes restricting control of hosts in the external database access list and limiting FMC management interface exposure to the public internet to reduce attack surface.
Description
A critical vulnerability exists in the External Database Access feature of Cisco Secure Firewall Management Center (FMC) Software that allows an unauthenticated remote attacker to execute arbitrary commands as root. The flaw arises from insecure deserialization of a user-supplied Java byte stream from a host configured in the external database access list. Exploitation requires control over a host in this access list and involves sending a crafted serialized Java byte stream to a specific TCP port. The vulnerability has a CVSS score of 9.8, indicating severe impact. The attack surface is reduced if the FMC management interface is not exposed to the public internet. No patch or remediation information is currently provided.