CVE-2026-20083: Cisco IOS XE Software DoS Vulnerability

CVE-2026-20083 Overview

A vulnerability in the Secure Copy Protocol (SCP) server feature of Cisco IOS XE Software could allow an authenticated, local attacker with low privileges to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to improper handling of a malformed SCP request. An attacker could exploit this vulnerability by issuing a crafted command through SSH. A successful exploit could allow the attacker to cause the device to reload unexpectedly, resulting in a DoS condition.

Critical Impact

Successful exploitation causes the affected Cisco IOS XE device to reload unexpectedly, resulting in network disruption and potential service outages for all traffic routed through the device.

Affected Products

• Cisco IOS XE Software with SCP server feature enabled
• Network devices running vulnerable versions of Cisco IOS XE
• Cisco routers and switches with SSH access configured

Discovery Timeline

• 2026-03-25 - CVE-2026-20083 published to NVD
• 2026-03-26 - Last updated in NVD database

Technical Details for CVE-2026-20083

Vulnerability Analysis

This vulnerability falls under CWE-235 (Improper Handling of Extra Parameters), indicating that the SCP server component within Cisco IOS XE Software fails to properly validate or sanitize malformed SCP requests. When an authenticated attacker with low-level privileges sends a specially crafted command through an established SSH session, the improper handling mechanism triggers an unrecoverable error condition that forces the device to reload.

The attack requires local access, meaning the attacker must first authenticate to the device via SSH before attempting exploitation. While this reduces the attack surface compared to remotely exploitable vulnerabilities, low-privilege authenticated users who should not have the ability to disrupt network operations can leverage this flaw to cause significant availability impact.

Root Cause

The root cause of this vulnerability is improper input validation in the SCP server feature of Cisco IOS XE Software. Specifically, the SCP request handler does not adequately process malformed requests, leading to an unhandled exception or resource corruption that triggers a device reload. The vulnerability exists in the parameter parsing logic where extra or malformed parameters in SCP requests are not properly rejected or sanitized before processing.

Attack Vector

The attack vector is local, requiring the attacker to have authenticated SSH access to the target Cisco IOS XE device. The exploitation process involves:

1. The attacker establishes an SSH connection to the vulnerable device using valid credentials (even with low-privilege access)
2. Once authenticated, the attacker issues a specially crafted SCP command containing malformed parameters
3. The SCP server component fails to properly handle the malformed request
4. The improper handling causes an internal error that forces the device to reload
5. During the reload process, all network traffic through the device is disrupted

The vulnerability requires authentication (PR:L), has no user interaction requirement, and the scope is changed (S:C), meaning the vulnerability in the SCP server component affects resources beyond its security scope by impacting the entire device's availability.

Detection Methods for CVE-2026-20083

Indicators of Compromise

• Unexpected device reloads coinciding with SCP or SSH activity in system logs
• Crash dump files indicating SCP-related processes or memory corruption
• Repeated authentication attempts followed by device crashes
• Abnormal SCP command patterns in SSH session logs

Detection Strategies

• Monitor system logs for crash events correlating with SCP server activity using keywords like SCP, reload, and crash
• Implement syslog forwarding to a SIEM to correlate SSH authentication events with subsequent device reloads
• Configure SNMP traps for unexpected reload events on Cisco IOS XE devices
• Review command accounting logs for unusual or malformed SCP commands from low-privilege users

Monitoring Recommendations

• Enable AAA command accounting to log all commands executed via SSH sessions
• Configure centralized logging to capture and retain device crash information
• Set up automated alerts for device reload events during unexpected maintenance windows
• Monitor for patterns of SSH authentication followed by rapid disconnection and device unavailability

How to Mitigate CVE-2026-20083

Immediate Actions Required

• Review the Cisco Security Advisory for specific remediation guidance
• Disable the SCP server feature if not required for operations until patches can be applied
• Restrict SSH access to only trusted administrators and management networks
• Implement access control lists (ACLs) to limit which hosts can establish SSH connections

Patch Information

Cisco has released a security advisory addressing this vulnerability. Administrators should consult the Cisco Security Advisory cisco-sa-scp-dos-duAdXtCg for specific fixed software versions and upgrade guidance. It is recommended to upgrade to a fixed release of Cisco IOS XE Software as soon as possible after testing in a non-production environment.

Workarounds

• Disable the SCP server feature using no ip scp server enable if SCP functionality is not required
• Implement strict access controls limiting SSH access to only necessary administrative personnel
• Use TACACS+ or RADIUS to enforce role-based access control and audit command execution
• Consider using alternative secure file transfer methods such as SFTP through a dedicated management interface

# Disable SCP server feature as a workaround
configure terminal
no ip scp server enable
end
write memory

# Restrict SSH access to management subnet only
configure terminal
access-list 10 permit 10.0.0.0 0.0.0.255
line vty 0 15
access-class 10 in
end
write memory