CVE-2020-14093 in Mutt
Summary
by MITRE
Mutt before 1.14.3 allows an IMAP fcc/postpone man-in-the-middle attack via a PREAUTH response.
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Analysis
by VulDB Data Team • 06/15/2020
The vulnerability identified as CVE-2020-14093 represents a critical security flaw in the Mutt email client software affecting versions prior to 1.14.3. This vulnerability specifically targets the IMAP protocol implementation within Mutt, creating a man-in-the-middle attack vector that can compromise email communications. The flaw manifests during the IMAP connection establishment process when the client receives a PREAUTH response from the mail server, which allows an attacker positioned between the client and server to intercept and manipulate email transmission processes.
The technical implementation of this vulnerability stems from insufficient validation of the IMAP PREAUTH response mechanism within Mutt's IMAP handling code. When an IMAP server sends a PREAUTH response, it indicates that the server has already authenticated the client, but Mutt's implementation fails to properly verify the authenticity of this response. This incomplete validation allows an attacker to inject malicious responses during the initial connection phase, potentially enabling them to intercept email messages destined for the FCC (file copy) or postpone functionality. The vulnerability operates at the protocol level, exploiting the trust model inherent in IMAP connections where the client assumes the server's PREAUTH response without adequate cryptographic verification.
From an operational impact perspective, this vulnerability compromises the integrity and confidentiality of email communications when users employ Mutt's IMAP functionality with servers that may be compromised or when attackers are present in the network path. The man-in-the-middle attack capability allows adversaries to potentially access sensitive email content, manipulate message routing, and interfere with email storage operations. Attackers can exploit this vulnerability to capture emails that would normally be stored in the FCC folder or to delay message delivery through the postpone mechanism, creating potential for information leakage or communication disruption. The impact extends beyond individual users to organizations that rely on Mutt for secure email communication, particularly in environments where email integrity is paramount.
Mitigation strategies for CVE-2020-14093 primarily involve updating to Mutt version 1.14.3 or later, which includes proper validation of PREAUTH responses and enhanced IMAP security measures. Organizations should also implement additional network security controls such as encrypted connections using TLS/SSL for IMAP communications, network monitoring to detect unusual connection patterns, and regular security assessments of email infrastructure. The vulnerability aligns with CWE-295 which addresses improper certificate validation, and represents a significant concern from an ATT&CK framework perspective under the T1566 technique for credential access through network sniffing and man-in-the-middle attacks. System administrators should also consider implementing email encryption solutions such as PGP or S/MIME to add additional layers of protection beyond the client-side fix, ensuring that even if the vulnerability is exploited, the email content remains protected.