CVE-2020-29547 in Citadel
Summary
by MITRE • 05/29/2023
An issue was discovered in Citadel through webcit-926. Meddler-in-the-middle attackers can pipeline commands after POP3 STLS, IMAP STARTTLS, or SMTP STARTTLS commands, injecting cleartext commands into an encrypted user session. This can lead to credential disclosure.
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Analysis
by VulDB Data Team • 05/30/2023
This vulnerability exists in the Citadel email client software through the webcit component version 926 and earlier, representing a critical security flaw that undermines the integrity of encrypted communication channels. The issue specifically affects protocols that utilize TLS encryption for securing email communications including POP3 STLS, IMAP STARTTLS, and SMTP STARTTLS commands. Attackers can exploit this weakness through a man-in-the-middle position to inject cleartext commands into established encrypted sessions, effectively bypassing the security measures designed to protect user credentials and sensitive data. The vulnerability stems from improper handling of command pipelining during the TLS negotiation process, allowing malicious actors to manipulate the communication flow.
The technical implementation of this flaw involves the attacker positioning themselves between the client and server during the initial TLS establishment phase. When users initiate POP3 STLS, IMAP STARTTLS, or SMTP STARTTLS commands, the system should maintain a secure encrypted channel for subsequent commands. However, the vulnerability permits attackers to inject malicious commands that execute within the encrypted session context, effectively allowing credential disclosure and potential unauthorized access to email accounts. This represents a significant violation of the principle of least privilege and secure communication protocols, as the attacker can manipulate commands that should remain isolated within the encrypted channel. The flaw is categorized under CWE-310 as a Cryptographic Vulnerability, specifically related to improper handling of encrypted sessions and command execution within TLS contexts.
The operational impact of this vulnerability is severe for organizations relying on Citadel email systems, as it enables attackers to compromise user accounts without requiring sophisticated attack vectors or significant resources. Once an attacker successfully injects commands into the encrypted session, they can potentially access email contents, extract authentication credentials, and perform unauthorized actions within user accounts. The attack requires only a passive position in the network traffic flow, making it particularly dangerous for environments where network monitoring is insufficient or where users connect through untrusted networks such as public Wi-Fi. This vulnerability directly relates to ATT&CK technique T1566 which involves credential harvesting through phishing or network attacks, and specifically targets the credential access phase of the attack lifecycle.
Mitigation strategies for this vulnerability require immediate patching of the webcit component to version 927 or later, which contains the necessary fixes for proper TLS session handling and command pipelining restrictions. Organizations should implement network monitoring solutions that can detect anomalous command sequences and unusual TLS handshake patterns that might indicate exploitation attempts. Additionally, administrators should consider implementing mandatory TLS enforcement policies and disable legacy protocols that do not properly support secure command handling. The fix addresses the root cause by ensuring proper session isolation during TLS negotiation and preventing command injection attacks that could occur during the transition from cleartext to encrypted communication states. Regular security audits should verify that all email clients and servers properly handle TLS commands and that no similar vulnerabilities exist in other components of the email infrastructure.