CVE-2023-28807 in ZIA
Summary
by MITRE • 01/31/2024
In Zscaler Internet Access (ZIA) a mismatch between Connect Host and Client Hello's Server Name Indication (SNI) enables attackers to evade network security controls by hiding their communications within legitimate traffic.
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Analysis
by VulDB Data Team • 02/22/2024
The vulnerability identified as CVE-2023-28807 affects Zscaler Internet Access (ZIA) systems and represents a significant security flaw in the handling of SSL/TLS handshake procedures. This issue stems from a critical mismatch between the Connect Host parameter and the Server Name Indication (SNI) field present in the Client Hello message during the TLS negotiation process. The fundamental problem occurs when the SNI value embedded in the initial client handshake does not align with the actual destination host that the connection is attempting to reach, creating a discrepancy that can be exploited by malicious actors to bypass security controls.
The technical implementation of this vulnerability exploits the inherent trust relationships within SSL/TLS protocols where security appliances rely on accurate SNI values to make informed decisions about traffic routing and inspection. When the Connect Host parameter differs from the SNI value in the Client Hello message, the ZIA system may incorrectly classify the traffic as legitimate, allowing potentially malicious communications to slip through security controls undetected. This misalignment creates a tunneling opportunity where attackers can leverage the legitimate SNI values of trusted domains to mask their actual destination endpoints, effectively performing protocol-level evasion attacks.
The operational impact of this vulnerability extends beyond simple traffic inspection bypasses, as it fundamentally undermines the integrity of network security monitoring and control mechanisms. Attackers can exploit this weakness to establish covert channels within seemingly legitimate network traffic, potentially enabling data exfiltration, command and control communications, or other malicious activities while remaining undetected by security systems that depend on proper SNI validation. The vulnerability particularly affects organizations that rely heavily on ZIA for web traffic filtering, content inspection, and threat prevention, as it creates a potential pathway for attackers to circumvent established security policies and controls.
From a cybersecurity perspective, this vulnerability aligns with several established threat patterns documented in the MITRE ATT&CK framework, specifically relating to evasion techniques that involve manipulating protocol behaviors and exploiting trust relationships. The issue also corresponds to CWE-295, which addresses improper certificate validation, and CWE-312, concerning the exposure of sensitive information through cleartext transmission. Organizations implementing ZIA solutions must consider this vulnerability as part of their broader security posture assessment, particularly in environments where strict network monitoring and traffic inspection are critical for compliance and threat detection purposes.
Mitigation strategies for CVE-2023-28807 should focus on implementing strict validation controls that enforce consistency between Connect Host parameters and SNI values during TLS handshakes. Security administrators should configure ZIA appliances to enforce strict SNI validation policies and implement additional monitoring mechanisms to detect anomalous SNI behavior patterns. Organizations should also consider deploying supplementary security controls such as deep packet inspection, traffic flow analysis, and anomaly detection systems that can identify potential exploitation attempts. Additionally, regular security assessments and penetration testing should be conducted to verify that the implemented controls effectively prevent this type of protocol-level evasion attack.