CVE-2019-18928 in IMAP
Summary
by MITRE
Cyrus IMAP 2.5.x before 2.5.14 and 3.x before 3.0.12 allows privilege escalation because an HTTP request may be interpreted in the authentication context of an unrelated previous request that arrived over the same connection.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 01/23/2025
The vulnerability identified as CVE-2019-18928 represents a critical privilege escalation flaw within Cyrus IMAP server versions 2.5.x prior to 2.5.14 and 3.x prior to 3.0.12. This issue stems from a fundamental flaw in how the server handles concurrent HTTP requests over the same connection, creating a dangerous context mixing scenario that can be exploited by malicious actors. The vulnerability specifically affects the authentication handling mechanism where the server fails to properly isolate authentication contexts between different requests, leading to potential unauthorized access to system resources. This flaw operates at the protocol level and demonstrates a classic case of improper session management that can have severe implications for email server security.
The technical root cause of this vulnerability lies in the server's inability to maintain proper request isolation when multiple HTTP requests are processed over the same TCP connection. When a client establishes an HTTP connection to the Cyrus IMAP server, the server processes requests sequentially but fails to properly clear or reset the authentication context between requests. An attacker can exploit this by crafting a malicious HTTP request that, when processed over the same connection as a legitimate authenticated request, inherits the authentication context of the previous request. This creates a scenario where unauthenticated or low-privilege requests can effectively impersonate authenticated users, leading to privilege escalation. The vulnerability specifically impacts the HTTP interface of the IMAP server, making it particularly dangerous for environments where web-based email access is enabled.
The operational impact of CVE-2019-18928 extends beyond simple unauthorized access to encompass potential full system compromise and data breaches. An attacker who successfully exploits this vulnerability can gain elevated privileges within the email server environment, potentially allowing them to read, modify, or delete email messages, access user accounts, and even escalate to system-level privileges depending on the server configuration. This vulnerability is particularly concerning in enterprise environments where Cyrus IMAP servers are commonly deployed to handle sensitive corporate communications. The attack vector requires minimal privileges to initiate and can be automated, making it a significant threat to organizations that rely on email infrastructure for business operations. The vulnerability also affects the integrity of the authentication system, potentially allowing attackers to establish persistent access to the email server.
Organizations affected by CVE-2019-18928 should immediately implement the vendor-provided patches for Cyrus IMAP versions 2.5.14 and 3.0.12, which address the authentication context isolation issue through proper request handling and session management. Network segmentation and access controls should be reviewed to limit exposure of the IMAP server to untrusted networks, while monitoring systems should be enhanced to detect unusual authentication patterns or connection behaviors. Security teams should also consider implementing connection pooling restrictions and ensuring that HTTP interfaces are properly secured with additional authentication layers. From a compliance perspective, this vulnerability relates to CWE-284 Access Control Issues and aligns with ATT&CK techniques involving privilege escalation and credential access. Regular security audits and penetration testing should be conducted to identify similar context mixing vulnerabilities in other server applications, as this type of flaw can potentially exist in any system that handles concurrent requests over persistent connections.