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Cisco Secure FMC EUVDEUVD-2026-81116

| CVE-2026-20340 HIGH
Deserialization of Untrusted Data (CWE-502)
2026-09-16 cisco GHSA-xpr9-grjf-6fm6
8.8
CVSS 3.1 · NVD
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Severity by source

Vendor (cisco) PRIMARY
HIGH
qualitative
NVD
8.8 HIGH
AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
vuln.today AI
8.8 HIGH

Network-reachable web mgmt (AV:N/AC:L), PR:L because the minimum Security Analyst read-only role is required, no UI; deserialization yields root code exec so C/I/A:H; S:U kept per Cisco though app→root arguably S:C.

3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (cisco).

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

2
Analysis Generated
Sep 16, 2026 - 21:40 vuln.today
CVE Published
Sep 16, 2026 - 20:10 nvd
HIGH 8.8

DescriptionNVD

A vulnerability in Cisco Secure FMC Software could allow an authenticated, remote attacker to execute arbitrary commands at the root privilege level.

This vulnerability is due to unsecured deserialization of web-management user-controlled data. An attacker could exploit this vulnerability by authenticating to the device and sending a crafted HTTP payload. A successful exploit could allow the attacker to save the crafted payload and then execute it on the underlying operating system as root. To exploit this vulnerability, the attacker must have valid credentials for a user account with at least the role of Security Analyst (read-only).

AnalysisAI

Authenticated remote code execution in Cisco Secure Firewall Management Center (FMC) lets a low-privileged web-management user turn a crafted HTTP request into root-level command execution on the underlying appliance. The flaw is an unsecured deserialization sink in the web-management interface (CWE-502): an attacker who can reach the FMC web UI and authenticate with credentials for at least the Security Analyst (read-only) role can save a malicious payload and get it executed as root, giving a complete compromise of confidentiality, integrity, and availability (CVSS 3.1 base 8.8, AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H). …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
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Delivery
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Exploit
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Execution
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Persist
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Impact
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Vulnerability AssessmentAI

Exploitation Requires (1) network reachability to the FMC web-management interface and (2) valid credentials for a user account with at least the Security Analyst (read-only) role - the lowest-privilege FMC role, so this is a very weak barrier rather than an admin gate. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment CVSS 3.1 base 8.8 (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) reflects a genuinely severe, network-reachable authenticated deserialization flaw yielding root code execution - the technical impact is total (C:H/I:H/A:H). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation The provided intelligence does not specify an exact fixed release: no vendor-released patch version is confirmed at time of analysis, and the only remediation source is Cisco's advisory at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fmc-mulivulns-4PsnFwvx (cisco-sa-fmc-mulivulns-4PsnFwvx), which should be consulted directly for the applicable fixed software matrix and upgrade path - do not assume any listed 7.x/10.0.x build is remediated without that confirmation. … Detailed patch versions, workarounds, and compensating controls in full report.

Recommended ActionAI

Within 24 hours, inventory every Cisco Secure Firewall Management Center appliance across the 7.0.x, 7.2.x, 7.3.x, 7.4.x, and 7.6.x release lines, immediately restrict management-interface reachability to a dedicated segmented administrative network or VPN with MFA, remove any internet-facing exposure, and audit all FMC accounts holding the Security Analyst role or equivalent read-only privileges so that stale, shared, or unnecessary credentials are disabled. …

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EUVD-2026-81116 vulnerability details – vuln.today

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