CVE-2026-20131
Cisco Secure Firewall Management Center Software Remote Code Execution Vulnerability
Description
A vulnerability in the web-based management interface of Cisco Secure Firewall Management Center (FMC) Software could allow an unauthenticated, remote attacker to execute arbitrary Java code as root on an affected device. This vulnerability is due to insecure deserialization of a user-supplied Java byte stream. An attacker could exploit this vulnerability by sending a crafted serialized Java object to the web-based management interface of an affected device. A successful exploit could allow the attacker to execute arbitrary code on the device and elevate privileges to root. Note: If the FMC management interface does not have public internet access, the attack surface that is associated with this vulnerability is reduced.
In plain language
AI Act nowCVE-2026-20131 is a critical, remotely exploitable bug in Cisco Secure Firewall Management Center (FMC) that lets an attacker run code as root without logging in—small businesses should treat this as urgent and act immediately if your FMC is reachable.
CVE-2026-20131 is an unauthenticated remote code execution in the Cisco Secure Firewall Management Center web-based management interface, triggered by insecure deserialization of attacker-supplied Java data leading to arbitrary code execution as root.
What to do now
- Check whether you run Cisco Secure Firewall Management Center (FMC) and confirm your software build with Cisco’s advisory for CVE-2026-20131 (look for “affected” vs “fixed”).
- Determine whether the FMC management interface is reachable from outside your network (internet or any third-party network paths). If it is reachable, assume you are within an attacker’s target zone.
- Apply the Cisco vendor remediation update for CVE-2026-20131 from trusted sources; if Cisco’s guidance says mitigations are unavailable in your environment, discontinue use of the product as directed.
- After updating, re-check exposure: verify network controls keep the management interface non-public and restrict access per vendor instructions.
CVSS Vector Breakdown
AV:NAttack VectorAC:LAttack ComplexityPR:NPrivileges RequiredUI:NUser InteractionS:CScopeC:HConfidentialityI:HIntegrityA:HAvailabilityWeaknesses
Affected Products
Exploitability
Required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Exploit details including PoC links, Metasploit modules, and scanner templates are available after registration.
View exploit detailsAttack Graph
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MITRE ATT&CK
3 techniquesReferences
- ThreatsDay: Odysseus RCE, Samsung One-Click Takeover, iCloud Backdoor Fight + 27 More Storiesen·The Hacker News· Roundup npm packages SideWinder
- Cisco FMC static credentials exploited by attackers (CVE-2026-20316)en-us·Help Net Security· Exploited Secure Firewall Management Center (FMC) network-edge
- Interlock and Rhysida Ransomware: IBM X-Force Maps a Shared Ecosystemen-us·Daily CyberSecurity (securityonline.info)· Research Interlock ransomware ransomware
- IT threat evolution in Q1 2026. Non-mobile statisticsen-us·Kaspersky Securelist· Exploited Kaspersky products Interlock
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