CVE-2020-10188: 
NixOS vulnerability analysis and mitigation

CVE-2020-10188 is a buffer overflow vulnerability discovered in telnetd in netkit telnet through version 0.17. The vulnerability allows remote attackers to execute arbitrary code via short writes or urgent data, specifically involving the netclear and nextitem functions (NVD, CVE). The vulnerability was disclosed on March 6, 2020, and affects various systems and software that implement the telnet protocol, including major vendors like Cisco, Palo Alto Networks, and Oracle.

The vulnerability exists in the utility.c file of telnetd, specifically in the netclear and nextitem functions. The nextitem function performs no bounds checking and can return pointers past the end of the region current. This can lead to buffer overflow when processing telnet protocol sequences, particularly when handling short writes or urgent data. The vulnerability has a CVSSv3.1 Base Score of 8.1 (HIGH) with network attack vector, high attack complexity, no privileges required, and high impacts on confidentiality, integrity, and availability (Palo Alto).

A successful exploitation of this vulnerability could allow remote attackers to execute arbitrary code on the affected system. The impact is particularly severe as it does not require authentication and can lead to complete system compromise. The vulnerability affects the telnet-based administrative management service, potentially giving attackers administrative access to affected systems (Palo Alto).

The primary mitigation is to disable the Telnet-based administrative management service completely. For systems where Telnet cannot be disabled immediately, vendors have released patches and updates. For example, Palo Alto Networks fixed this in PAN-OS versions 8.1.20, 9.0.14, 9.1.9, 10.0.6, and all later versions. Additionally, network access to the Telnet interface should be restricted following security best practices (Palo Alto). Fedora released updates for versions 30, 31, and 32 to address this vulnerability (Fedora Update).