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Cisco FMC EUVDEUVD-2026-81103

| CVE-2026-20324 CRITICAL
Missing Authorization (CWE-862)
2026-09-16 cisco GHSA-m3pq-vq89-c8m5
9.9
CVSS 3.1 · NVD
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Severity by source

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

Network sftunnel path (AV:N), low complexity (AC:L), requires valid credentials or a registered peer (PR:L), and a peer/user foothold escalating to root device compromise justifies S:C with full C:H/I:H/A:H.

3.1 AV:N/AC:L/PR:L/UI:N/S:C/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:H/SI:H/SA:H

Primary rating from Vendor (cisco).

CVSS VectorNVD

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

Lifecycle Timeline

3
Metadata Corrected
Sep 16, 2026 - 21:40 vuln.today
tag: Authentication Bypass removed
Analysis Generated
Sep 16, 2026 - 20:43 vuln.today
CVE Published
Sep 16, 2026 - 20:06 nvd
CRITICAL 9.9

DescriptionNVD

A vulnerability in the sftunnel inter-device communication protocol of Cisco Secure Firewall Management Center (FMC) Software could allow an authenticated, remote attacker to execute arbitrary commands as root.

This vulnerability exists because a registered sftunnel peer has incorrect permissions to write an arbitrary file to any location on the device. An attacker could exploit this vulnerability by hijacking the sftunnel communication connection or being a valid registered sftunnel peer and sending an sftunnel command to write a malicious file to the disk of an affected device. A successful exploit could allow the attacker to write a file to the device that is executed with root privileges. To exploit this vulnerability, the attacker must have valid user credentials on the affected device.

AnalysisAI

Authenticated remote code execution as root affects Cisco Secure Firewall Management Center (FMC) software. An attacker who possesses valid user credentials on the FMC - or who can hijack an established sftunnel peer connection - can send a crafted sftunnel command that writes a malicious file to any location on the device, and that file is then executed with root privileges (CVSS 9.9, CWE-862). …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
technique details hidden
Delivery
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Exploit
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Execution
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Impact
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Vulnerability AssessmentAI

Exploitation Exploitation requires the attacker to either possess valid user credentials on the affected Cisco Secure FMC or to control/hijack a registered sftunnel peer connection, then issue an sftunnel inter-device protocol command that writes an arbitrary file to disk; the planted file is subsequently executed with root privileges. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment This is a genuine high-priority vulnerability, not a high-CVSS-but-low-real-risk case. … 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 No exact fixed release version is provided in the available data; Cisco's advisory (cisco-sa-fmc-sftunn-codex-c3O4Jft2) should be consulted for the patched software version and any available hotfixes. … Detailed patch versions, workarounds, and compensating controls in full report.

Recommended ActionAI

Within 24 hours, inventory every Cisco Secure Firewall Management Center (FMC) deployment in the environment, record its exact software release, and confirm which accounts hold valid FMC user credentials; immediately reduce that population to the minimum necessary, rotate any shared or stale credentials, enforce multi-factor authentication where supported, and audit FMC audit/authentication logs for unexpected sftunnel activity or file writes. …

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EUVD-2026-81103 vulnerability details – vuln.today

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