CVE-2026-4942 in IBM
Summary
by MITRE • 07/17/2026
IBM i 7.6, 7.5, 7.4, and 7.3 could allow a remote attacker to send a specifically crafted message and downgrade the Transport Layer Security (TLS) protocol to a version disabled in the server configuration.
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Analysis
by VulDB Data Team • 07/17/2026
This vulnerability exists within IBM i operating systems versions 7.3 through 7.6, presenting a significant security risk that enables remote attackers to manipulate TLS protocol negotiations. The flaw allows adversaries to craft specific messages that can force the system to downgrade TLS connections to versions that have been explicitly disabled in the server configuration, effectively bypassing security controls designed to prevent insecure communications.
The technical implementation of this vulnerability stems from improper handling of TLS protocol version negotiation mechanisms within the IBM i secure communication stack. When a client attempts to establish a TLS connection, the system should enforce the configured minimum TLS version requirements and reject any attempts to downgrade to older, less secure versions. However, the flaw permits malicious actors to send specially crafted handshake messages that can override these security policies, potentially allowing connections to be established using deprecated TLS versions such as TLS 1.0 or 1.1 even when the server has explicitly disabled them.
From an operational impact perspective, this vulnerability creates multiple attack vectors for adversaries seeking to compromise secure communications on IBM i systems. The ability to downgrade TLS protocols opens the door for man-in-the-middle attacks where attackers can intercept and potentially modify encrypted traffic between clients and servers. This risk is particularly severe because it undermines fundamental security assumptions about TLS encryption strength, allowing attackers to exploit known vulnerabilities in older TLS versions such as POODLE, BEAST, or other protocol-level weaknesses that have been addressed in newer implementations.
The vulnerability aligns with CWE-327, which addresses the use of weak cryptographic algorithms and improper implementation of cryptographic protocols. It also maps to ATT&CK technique T1046 which covers network service scanning and T1566 which involves credential harvesting through social engineering or protocol manipulation. Organizations running IBM i systems in environments where secure communications are critical face elevated risk of data interception, session hijacking, and potential privilege escalation attacks that leverage the weakened TLS security posture.
Mitigation strategies should focus on immediate patch application from IBM as the primary remediation approach, combined with network-level monitoring to detect anomalous TLS handshake patterns. System administrators should also implement strict TLS configuration policies that prevent protocol downgrades regardless of client requests, and deploy network segmentation to limit exposure of critical systems. Additionally, organizations should conduct thorough security assessments to identify all systems running affected IBM i versions and ensure proper TLS version enforcement is implemented across all network services. The vulnerability demonstrates the critical importance of maintaining secure cryptographic protocol implementations and highlights the need for robust protocol negotiation controls that cannot be easily bypassed by malicious actors.