CVE-2020-3201 in IOS
Summary
by MITRE
A vulnerability in the Tool Command Language (Tcl) interpreter of Cisco IOS Software and Cisco IOS XE Software could allow an authenticated, local attacker with privileged EXEC credentials to cause a denial of service (DoS) condition on an affected system. The vulnerability is due to insufficient input validation of data passed to the Tcl interpreter. An attacker could exploit this vulnerability by executing crafted Tcl arguments on an affected device. An exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition.
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Analysis
by VulDB Data Team • 10/21/2020
The vulnerability identified as CVE-2020-3201 represents a critical security flaw within the Tool Command Language (Tcl) interpreter component of Cisco IOS and IOS XE software platforms. This weakness specifically targets authenticated local attackers who possess privileged EXEC credentials, creating a significant risk for network infrastructure devices. The vulnerability stems from inadequate input validation mechanisms within the Tcl interpreter, which fails to properly sanitize or verify data passed to this scripting component. Such insufficient validation creates an exploitable condition where maliciously crafted Tcl arguments can be executed against affected systems, potentially compromising the stability and availability of critical network infrastructure.
The technical implementation of this vulnerability manifests through the Tcl interpreter's failure to properly handle malformed or crafted input data, leading to unpredictable behavior within the system's execution environment. When an authenticated attacker with privileged access submits specially crafted Tcl commands, the interpreter processes these inputs without adequate safeguards, potentially triggering memory corruption or execution flow disruptions. The exploitation mechanism leverages the legitimate Tcl interpreter functionality while introducing malicious payloads that cause the system to enter an unrecoverable state. This results in the device experiencing a complete reload or reboot cycle, effectively creating a denial of service condition that can disrupt network operations and compromise service availability.
From an operational impact perspective, this vulnerability poses significant risks to network infrastructure reliability and business continuity. The DoS condition caused by the device reload can lead to extended network outages, particularly in mission-critical environments where continuous availability is paramount. Network administrators may experience service disruptions that require manual intervention to restore normal operations, potentially affecting multiple network services and users simultaneously. The vulnerability's requirement for authenticated access with privileged EXEC credentials limits its exposure compared to remote exploits, but it remains particularly dangerous in environments where privileged accounts are compromised or where insider threats exist. The impact extends beyond simple service disruption as the repeated exploitation can cause cumulative system instability and may mask other underlying security issues.
Organizations should implement immediate mitigations including applying the latest Cisco software patches and updates that address the input validation deficiencies in the Tcl interpreter. Network segmentation and access control measures should be enhanced to limit the number of users with privileged EXEC access, following the principle of least privilege. Monitoring systems should be configured to detect unusual Tcl interpreter activity or unauthorized privileged access attempts. The vulnerability aligns with CWE-20, which describes "Improper Input Validation," and represents a classic example of how inadequate sanitization can lead to system instability. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation and denial of service techniques, potentially enabling attackers to establish persistence through repeated exploitation. Regular security assessments and vulnerability scanning should be conducted to identify affected systems and ensure proper patch management protocols are maintained across all network infrastructure components.