CVE-2019-11494 in Dovecot
Summary
by MITRE
In the IMAP Server in Dovecot 2.3.3 through 2.3.5.2, the submission-login service crashes when the client disconnects prematurely during the AUTH command.
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Analysis
by VulDB Data Team • 09/15/2023
The vulnerability identified as CVE-2019-11494 represents a denial of service condition within Dovecot's IMAP server implementation that affects versions 2.3.3 through 2.3.5.2. This issue manifests specifically within the submission-login service component where the server experiences a crash when clients terminate their connection unexpectedly during the authentication process. The flaw demonstrates characteristics consistent with improper handling of connection states and resource management during protocol negotiation phases, creating a scenario where legitimate service availability is compromised through malicious or accidental client behavior.
The technical root cause of this vulnerability stems from inadequate error handling within the AUTH command processing within the submission-login service. When a client disconnects before completing the authentication sequence, the server fails to properly manage the cleanup of allocated resources and execution flow, resulting in an unhandled exception that terminates the service process. This behavior aligns with CWE-400, which categorizes improper handling of exceptional conditions, and specifically reflects issues related to resource management and exception handling in network services. The vulnerability operates at the application layer and requires minimal privileges to exploit, making it particularly concerning for systems where availability is critical.
The operational impact of CVE-2019-11494 extends beyond simple service disruption as it can be leveraged for sustained denial of service attacks against mail servers. Attackers can repeatedly trigger the crash condition by establishing connections and disconnecting prematurely during authentication, potentially causing service instability and resource exhaustion. This vulnerability affects email infrastructure components that rely on Dovecot's IMAP server functionality, particularly in enterprise environments where email services are mission-critical. The attack pattern corresponds to techniques described in the ATT&CK framework under T1499.004 for Network Denial of Service, where adversaries target application-level services to disrupt availability.
Mitigation strategies for this vulnerability should prioritize immediate patching of affected Dovecot installations to versions beyond 2.3.5.2 where the issue has been resolved. System administrators should implement monitoring solutions to detect unusual connection patterns and service restarts that may indicate exploitation attempts. Network-level protections including rate limiting and connection tracking can help reduce the impact of automated exploitation attempts. Additionally, implementing proper logging and alerting mechanisms around authentication service operations will enable rapid detection of potential exploitation. The fix implemented by Dovecot developers addresses the specific resource cleanup issue during premature client disconnections and includes proper exception handling to prevent service termination under these conditions, aligning with security best practices for robust application design and resilience against malformed input conditions.