CVE-2026-31798 in JumpServer
Summary
by MITRE • 03/13/2026
JumpServer is an open source bastion host and an operation and maintenance security audit system. Prior to v4.10.16-lts, JumpServer improperly validates certificates in the Custom SMS API Client. When JumpServer sends MFA/OTP codes via Custom SMS API, an attacker can intercept the request and capture the verification code BEFORE it reaches the user's phone. This vulnerability is fixed in v4.10.16-lts.
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Analysis
by VulDB Data Team • 03/20/2026
The vulnerability identified as CVE-2026-31798 affects JumpServer, an open source bastion host and operations security audit system that provides centralized access control and monitoring for enterprise infrastructure. This system serves as a critical security component that manages privileged access to network resources while maintaining detailed audit trails of all administrative activities. The vulnerability specifically impacts the Custom SMS API Client functionality within JumpServer's multi-factor authentication implementation, creating a significant security gap in the system's authentication mechanisms. Prior to version 4.10.16-lts, the software failed to properly validate SSL/TLS certificates when establishing connections to third-party SMS service providers, leaving the authentication pipeline susceptible to man-in-the-middle attacks. The flaw exists in the certificate validation process that occurs during the transmission of time-based one-time passwords and multi-factor authentication codes, which are essential components for securing privileged access to critical systems.
The technical implementation of this vulnerability stems from inadequate certificate validation within the Custom SMS API Client module of JumpServer. When the system sends verification codes via SMS for multi-factor authentication purposes, it establishes secure connections to external SMS service providers to deliver these codes to users. However, the software's certificate validation mechanism fails to properly verify the authenticity and integrity of the SSL/TLS certificates presented by these external services. This weakness allows an attacker positioned within the network traffic path to perform SSL stripping attacks or present fraudulent certificates that appear legitimate to the JumpServer system. The vulnerability specifically affects the certificate validation routines that should ensure the connection is established with the intended service provider rather than an attacker-controlled intermediary. This improper validation enables attackers to intercept and capture the one-time verification codes before they reach the intended recipients, effectively compromising the multi-factor authentication security controls.
The operational impact of this vulnerability extends far beyond simple credential theft, as it fundamentally undermines the security posture of organizations relying on JumpServer for privileged access management. When attackers successfully intercept MFA/OTP codes, they can bypass critical authentication controls that are designed to prevent unauthorized access to sensitive systems and data. This vulnerability creates a pathway for attackers to escalate privileges and gain access to critical infrastructure, potentially leading to data breaches, system compromise, and unauthorized administrative access. The attack vector is particularly concerning because it operates at the network level, where attackers can leverage existing network access to intercept communications without requiring additional authentication credentials or complex exploitation techniques. The vulnerability affects organizations that depend on SMS-based MFA as part of their security infrastructure, creating a window of opportunity for attackers to exploit the authentication gap while maintaining the appearance of legitimate system communications.
Organizations using JumpServer versions prior to 4.10.16-lts should immediately implement the available patch to address this vulnerability and enhance their overall security posture. The fix in version 4.10.16-lts specifically addresses the certificate validation logic within the Custom SMS API Client, ensuring that all SSL/TLS certificates are properly verified before establishing secure connections to external SMS service providers. Security teams should also consider implementing additional monitoring measures to detect potential interception attempts and establish network-level controls to prevent unauthorized access to the JumpServer infrastructure. This vulnerability aligns with CWE-295, which addresses improper certificate validation in security protocols, and represents a clear violation of the principle of least privilege by allowing unauthorized interception of authentication tokens. The remediation process should include thorough testing of the patched environment to ensure that legitimate SMS delivery continues to function properly while the certificate validation has been strengthened. Organizations should also review their broader security policies regarding multi-factor authentication implementation and consider implementing additional layers of protection such as hardware security modules or more robust authentication methods to further reduce the attack surface.