CVE-2023-42818 in JumpServer
Summary
by MITRE • 10/25/2023
JumpServer is an open source bastion host. When users enable MFA and use a public key for authentication, the Koko SSH server does not verify the corresponding SSH private key. An attacker could exploit a vulnerability by utilizing a disclosed public key to attempt brute-force authentication against the SSH service This issue has been patched in versions 3.6.5 and 3.5.6. Users are advised to upgrade. There are no known workarounds for this issue.
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Analysis
by VulDB Data Team • 03/25/2025
The vulnerability identified as CVE-2023-42818 affects JumpServer, an open source bastion host solution that provides secure access management for enterprise environments. This security flaw specifically impacts the Koko SSH server component within the JumpServer ecosystem, creating a significant authentication weakness that could compromise the security posture of organizations relying on this platform. The vulnerability manifests when users configure multi-factor authentication and employ public key authentication methods, which are standard security practices for securing remote access services. The issue represents a critical failure in the authentication verification process where the system fails to validate the corresponding private key associated with a disclosed public key, creating an exploitable gap in the security architecture.
The technical flaw in CVE-2023-42818 stems from improper key validation mechanisms within the Koko SSH server implementation. When a user enables multi-factor authentication and configures public key authentication, the system should verify that the private key corresponding to the public key presented during authentication actually exists and is valid. However, the vulnerability allows an attacker to exploit a disclosed public key to conduct brute-force authentication attempts against the SSH service without proper verification of the private key component. This creates a scenario where the authentication process becomes vulnerable to credential stuffing and brute-force attacks, as the system accepts public keys without ensuring their corresponding private keys are properly validated. The flaw essentially bypasses the expected security controls that should prevent unauthorized access attempts, allowing attackers to potentially gain access to systems through compromised or improperly validated authentication credentials.
The operational impact of this vulnerability extends beyond simple authentication bypass scenarios and represents a significant risk to enterprise security infrastructure. Organizations using JumpServer with MFA enabled and public key authentication may experience unauthorized access to their systems, potentially leading to data breaches, privilege escalation, and lateral movement within network environments. The vulnerability affects the core security functionality of the bastion host, which is designed to provide secure access control and audit capabilities for administrative operations. Attackers could exploit this weakness to establish persistent access to target systems, particularly in environments where JumpServer serves as the primary access point for system administrators and privileged users. The implications are particularly severe given that JumpServer is commonly deployed in enterprise environments where it controls access to critical infrastructure and sensitive systems.
The vulnerability aligns with CWE-326, which addresses the issue of inadequate encryption strength, and represents a failure in proper cryptographic key management and validation processes. From an attack perspective, this flaw maps to ATT&CK technique T1210, which covers exploitation of remote services through the use of valid credentials, and T1078, which covers valid accounts as a means of gaining access. Organizations should implement immediate mitigations including upgrading to JumpServer versions 3.6.5 or 3.5.6, which contain the necessary patches to address the key validation issue. Additionally, security teams should review existing public key configurations and implement additional monitoring for authentication attempts, particularly those involving public key authentication methods. The lack of known workarounds means that organizations must prioritize the upgrade process to remediate this vulnerability effectively. Security professionals should also consider implementing network-level controls and additional authentication layers to reduce the attack surface while awaiting the upgrade deployment. The vulnerability underscores the importance of proper key validation mechanisms in authentication systems and highlights the need for comprehensive security testing of cryptographic implementations within access management solutions.