CVE-2026-20083 in IOS XE
Summary
by MITRE • 03/25/2026
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.
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Analysis
by VulDB Data Team • 04/12/2026
The vulnerability identified as CVE-2026-20083 represents a critical denial of service weakness within Cisco IOS XE Software's Secure Copy Protocol implementation. This flaw specifically affects the SCP server functionality that operates within the network operating system, creating an avenue for authenticated local attackers to disrupt normal device operations. The vulnerability stems from inadequate input validation mechanisms that fail to properly process malformed SCP requests, which are typically used for secure file transfers between network devices. When an attacker crafts a specifically designed SCP request through an SSH session, the system's failure to handle such malformed input results in unexpected behavior that ultimately leads to device instability.
The technical exploitation of this vulnerability occurs through a carefully constructed SCP request that bypasses normal protocol validation checks within the IOS XE software stack. This malformed request triggers an improper state handling mechanism within the SCP server component, causing the system to enter an inconsistent operational state. The attack vector requires local authentication with low privileges, meaning that an attacker must first establish a valid SSH session to the device before attempting the exploit. This prerequisite significantly limits the attack surface but does not eliminate the risk, as many network devices maintain active SSH sessions for legitimate administrative purposes. The vulnerability manifests as an unexpected device reload, which constitutes a complete denial of service condition that can disrupt network operations and potentially affect critical infrastructure services.
The operational impact of this vulnerability extends beyond simple service disruption, as it can cause cascading effects throughout network infrastructure that relies on the affected device for routing, switching, or security functions. Network administrators may experience unexpected downtime during critical maintenance windows or when automated processes depend on stable device operation. The vulnerability's classification aligns with CWE-20, which addresses "Improper Input Validation" in software systems, and represents a classic example of how malformed input processing can lead to system instability. From an adversarial perspective, this vulnerability fits within ATT&CK technique T1499.004, which covers "Endpoint Denial of Service" through resource consumption or system instability. The DoS condition caused by the unexpected reload can result in configuration loss, service interruption, and potential security gaps during the recovery period.
Mitigation strategies for CVE-2026-20083 should prioritize immediate software updates from Cisco to address the root cause of the malformed input handling issue. Network administrators must ensure that all affected Cisco IOS XE devices receive the appropriate security patches that correct the SCP server's input validation mechanisms. Additionally, implementing network access controls and monitoring systems can help detect anomalous SCP request patterns that might indicate exploitation attempts. The principle of least privilege should be enforced to limit the number of users with local access to devices running affected software versions, thereby reducing the attack surface. Network segmentation and monitoring solutions should be deployed to track SSH session activity and identify potentially malicious SCP requests. Organizations should also consider implementing automated patch management processes to ensure timely deployment of security updates across all network infrastructure components. Regular vulnerability assessments and security audits should be conducted to identify similar weaknesses in other network protocols and services that may present comparable risks.