CVE-2016-10027 in Smack
Summary
by MITRE
Race condition in the XMPP library in Smack before 4.1.9, when the SecurityMode.required TLS setting has been set, allows man-in-the-middle attackers to bypass TLS protections and trigger use of cleartext for client authentication by stripping the "starttls" feature from a server response.
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Analysis
by VulDB Data Team • 10/25/2024
The vulnerability identified as CVE-2016-10027 represents a critical race condition within the Smack XMPP library version 4.1.8 and earlier, specifically affecting implementations that utilize SecurityMode.required TLS settings. This flaw creates a significant security weakness in the XMPP protocol's transport layer security mechanisms, where an attacker can manipulate the TLS negotiation process to bypass established security protections. The vulnerability manifests when the library processes server responses that have had the "starttls" feature stripped, allowing for a man-in-the-middle attack scenario that ultimately results in cleartext communication being accepted instead of the expected encrypted TLS connection. The race condition occurs during the asynchronous processing of TLS handshake sequences, where the timing of feature negotiation and connection establishment creates a window of opportunity for malicious interference.
The technical exploitation of this vulnerability relies on the library's improper handling of the TLS feature negotiation process within the XMPP protocol framework. When SecurityMode.required is configured, the library should enforce mandatory TLS usage for all client-server communications, but due to the race condition, it fails to properly validate that the TLS handshake has been completed successfully before proceeding with authentication. This flaw is categorized under CWE-362, which describes a race condition vulnerability, and specifically aligns with the ATT&CK technique T1566.002 related to spearphishing via social media. The attacker must intercept the initial server response and remove the starttls feature before the client processes it, creating a window where the client may proceed with cleartext authentication instead of establishing a secure TLS connection. This vulnerability directly impacts the integrity of the security model by allowing attackers to downgrade the security level of communications from encrypted to plaintext, potentially exposing sensitive authentication credentials and session data.
The operational impact of this vulnerability extends beyond simple credential exposure, as it fundamentally undermines the security assurances provided by the XMPP protocol's TLS implementation. When exploited, attackers can intercept and modify communications between XMPP clients and servers, potentially gaining access to user credentials, private messages, and other sensitive data transmitted through the protocol. The vulnerability affects any application or service utilizing Smack library versions prior to 4.1.9 that have configured SecurityMode.required, making it particularly concerning for enterprise messaging systems, instant messaging platforms, and any security-sensitive XMPP implementations. The race condition nature means that successful exploitation requires precise timing and network interception capabilities, but the vulnerability remains persistent across multiple deployment scenarios. Organizations using affected versions of the Smack library should immediately implement mitigation strategies including upgrading to version 4.1.9 or later, implementing additional network monitoring, and reviewing their security configurations to ensure proper TLS enforcement mechanisms are in place.
The remediation approach for this vulnerability centers on upgrading the Smack library to version 4.1.9 or higher, which includes fixes specifically addressing the race condition in TLS feature negotiation. Additionally, administrators should review their security configurations to ensure that SecurityMode.required is properly enforced and that the library's TLS validation mechanisms are functioning correctly. Network security controls should be enhanced to detect and prevent manipulation of XMPP server responses, including monitoring for unusual patterns in feature negotiation and implementing stricter TLS certificate validation policies. The vulnerability serves as a reminder of the importance of proper synchronization mechanisms in security-critical code paths and highlights the need for comprehensive testing of security features under various network conditions and timing scenarios. Organizations should also consider implementing automated security scanning processes to identify and remediate similar vulnerabilities in other protocol libraries and security implementations within their infrastructure.