CVE-2020-12673 in Dovecot
Summary
by MITRE
In Dovecot before 2.3.11.3, sending a specially formatted NTLM request will crash the auth service because of an out-of-bounds read.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 11/08/2020
The vulnerability CVE-2020-12673 represents a critical out-of-bounds read flaw in Dovecot authentication services that affects versions prior to 2.3.11.3. This issue specifically manifests when the authentication service processes specially crafted NTLM requests, which are commonly used in Windows authentication protocols. The flaw occurs within the NTLM authentication module where improper input validation leads to memory access violations. The out-of-bounds read vulnerability allows an attacker to manipulate the authentication service by sending malformed NTLM packets that cause the application to access memory locations beyond the allocated buffer boundaries. This type of vulnerability falls under the CWE-125 out-of-bounds read category, which is classified as a memory safety issue that can lead to system instability and potential remote code execution. The vulnerability is particularly concerning because it affects the core authentication functionality of Dovecot, which is widely deployed in email server environments and other systems relying on secure authentication mechanisms. The impact extends beyond simple service disruption as the crash can be leveraged to cause denial of service attacks against email servers and other Dovecot-based services. According to ATT&CK framework, this vulnerability maps to T1190 - Exploit Public-Facing Application, as it represents an exploitable weakness in a publicly accessible authentication service. The NTLM protocol implementation in Dovecot fails to properly validate the length and structure of incoming authentication requests, creating a path for malicious actors to trigger the buffer overflow condition. This flaw demonstrates the importance of robust input validation in authentication protocols, as even seemingly benign protocol interactions can be weaponized to compromise service availability. The vulnerability is particularly dangerous in environments where Dovecot serves as a critical authentication backend for email systems, as it can be exploited to deny legitimate users access to email services and potentially disrupt business operations. Security researchers have noted that the out-of-bounds read occurs during the processing of NTLM authentication challenges, where the authentication service attempts to parse and validate incoming authentication tokens without adequate bounds checking. The crash results from the service reading memory beyond the intended buffer limits, which can cause unpredictable behavior including service termination and system instability. Organizations using Dovecot versions prior to 2.3.11.3 should immediately implement mitigations including applying the official patches, implementing network segmentation to limit access to authentication services, and monitoring for suspicious authentication attempts. The vulnerability highlights the need for comprehensive security testing of authentication protocols and demonstrates how protocol-level flaws can have cascading effects on overall system security. Proper input validation and memory safety practices are essential to prevent such issues from being exploited in production environments, particularly in critical infrastructure components like email servers and authentication backends.