CVE-2026-123848 in IntelliJ IDEA
Summary
by MITRE • 11/06/2026
In JetBrains IntelliJ IDEA before 2026.3 host name verification was missing for server TLS certificates
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 11/06/2026
The vulnerability identified in versions of JetBrains IntelliJ IDEA prior to version 2026.3 involves a critical deficiency in the implementation of Transport Layer Security (TLS) certificate validation during remote connections. Specifically, the application failed to perform hostname verification when establishing secure communications with external servers. This oversight means that while the cryptographic handshake may have completed successfully and encrypted data was transmitted, the client did not verify whether the server's presented X.509 certificate actually matched the domain name it connected to. In a standard TLS implementation, this step is essential for preventing man-in-the-middle attacks where an attacker might present a validly signed but incorrectly named certificate to impersonate a legitimate service.
From a technical perspective, this flaw represents a classic instance of incomplete verification of authentication credentials within a secure channel. The Java Secure Socket Extension (JSSE) and similar TLS libraries typically require developers to explicitly implement or ensure default hostname verifiers are active. By omitting this check, IntelliJ IDEA effectively trusted any certificate presented by the server as long as it was signed by a recognized Certificate Authority, regardless of whether the subject alternative names or common name in the certificate matched the intended host. This creates a significant attack surface where an adversary positioned on the network path could intercept traffic and inject their own malicious certificates without triggering security warnings or connection failures within the IDE environment.
The operational impact of this vulnerability is severe, particularly given that IntelliJ IDEA is often used to access sensitive remote repositories, cloud services, JetBrains account servers, and internal corporate tools. An attacker exploiting this flaw could perform a man-in-the-middle attack to steal authentication tokens, read proprietary source code being synchronized or pushed from the IDE, or inject malicious plugins and dependencies into the development workflow. Since developers frequently store credentials and project data within the integrated environment, compromising these connections allows for extensive data exfiltration and potential supply chain compromise at the developer workstation level. This aligns with CWE-295 Improper Certificate Validation and is mapped to MITRE ATT&CK technique T1078 Valid Accounts if used in conjunction with credential theft or T1041 Exfiltration Over C2 Channel for data removal.
To mitigate this risk, users must upgrade JetBrains IntelliJ IDEA to version 2026.3 or any later release where the hostname verification logic has been corrected and enforced by default. Until such an update is applied in controlled environments, network-level controls should be employed, such as strict firewall rules limiting outbound connections from development machines to only known trusted domains, and the use of internal PKI solutions that can monitor for anomalous certificate presentations. Additionally, enabling detailed logging on proxy servers or firewalls may help detect attempts to connect using mismatched certificates during this interim period.