CVE-2020-29379 in V1600D4L
Summary
by MITRE • 11/29/2020
An issue was discovered on V-SOL V1600D4L V1.01.49 and V1600D-MINI V1.01.48 OLT devices. During the process of updating the firmware, the update script starts a telnetd -l /bin/sh process that does not require authentication for TELNET access.
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Analysis
by VulDB Data Team • 12/11/2020
This vulnerability exists in V-SOL OLT devices running specific firmware versions where the firmware update process creates an unauthenticated telnet daemon instance. The flaw occurs when the update script launches telnetd with the -l /bin/sh option, effectively creating a shell access point without any authentication requirements. This represents a critical security weakness that directly violates fundamental security principles of access control and privilege management. The vulnerability stems from improper privilege separation during firmware operations, where administrative functions are executed with elevated privileges while simultaneously exposing a fully functional shell to any network entity with access to the telnet port.
The technical implementation of this flaw involves the update script executing a telnet daemon with root-level shell access, creating an attack surface that allows unauthorized remote access to the device's command shell. This configuration enables attackers to execute arbitrary commands with the highest possible privileges, effectively providing complete system compromise. The vulnerability is particularly concerning because it operates during a legitimate administrative process, making it difficult to detect through normal security monitoring. The lack of authentication requirements means that any attacker with network access to the device can immediately gain root shell access, bypassing all normal security controls and authentication mechanisms.
From an operational perspective, this vulnerability creates an immediate and severe risk to network infrastructure security. Organizations relying on these OLT devices face potential complete system compromise, data exfiltration, and network disruption. The attack surface extends beyond simple unauthorized access to include potential lateral movement within the network, as the compromised device could serve as a pivot point for accessing other network segments. This vulnerability directly impacts the CIA triad by compromising confidentiality through unauthorized data access, integrity through potential malicious command execution, and availability through possible service disruption. The flaw affects network operators who may not realize their systems are compromised until after an attack has occurred, as the telnet daemon operates silently in the background.
Mitigation strategies should focus on immediate network segmentation and access control measures to prevent unauthorized network access to these devices. Network administrators should implement firewall rules to block telnet access to affected devices and consider disabling the firmware update functionality until patches are applied. The vulnerability aligns with CWE-310 (Cryptographic Issues) and CWE-284 (Improper Access Control) categories, representing a clear violation of secure coding practices and access control mechanisms. Organizations should also consider implementing network monitoring to detect unauthorized telnet connections and establish baseline network behavior for these devices. The ATT&CK framework categorizes this vulnerability under T1021.004 (SSH and Telnet) and T1059.004 (Unix Shell) techniques, highlighting the potential for privilege escalation and command execution. Regular firmware updates and security audits should be implemented to prevent similar issues in the future, with particular attention to how administrative processes handle privilege escalation and service exposure during critical operations.