Description

In JetBrains IntelliJ IDEA before 2026.3 host name verification was missing for server TLS certificates

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.4",
  "pubDate": "2026-11-06T17:17:23.717Z",
  "pubdate": "2026-11-06T17:17:23.717Z",
  "executiveSummary": "A critical security vulnerability exists in JetBrains IntelliJ IDEA versions prior to 2026.3, characterized by the absence of host name verification during the TLS handshake process.\nThis vulnerability, rooted in improper certificate validation, allows an attacker in a privileged network position (such as a Man-in-the-Middle position) to intercept encrypted traffic or present a fraudulent server certificate to the application.\nBecause the client software fails to verify that the certificate's Common Name (CN) or Subject Alternative Name (SAN) matches the expected hostname, the application may inadvertently establish secure connections with malicious servers posing as legitimate endpoints.\nThe risk implication is significant, as it facilitates the potential interception of sensitive information, such as authentication tokens, credentials, or proprietary source code transmitted over TLS-protected connections.\nThe attack does not require prior authentication or elevated privileges within the application itself; it relies purely on the attacker's ability to manipulate network traffic between the client and the intended server.\nSuccessful exploitation requires the attacker to actively influence network routing or perform DNS spoofing to redirect traffic through a proxy or malicious node controlled by the adversary.",
  "technicalDetails": "The root cause of this vulnerability is the failure of the TLS implementation within IntelliJ IDEA to enforce RFC 6125 compliance regarding the verification of server identities.\nDuring the standard TLS/SSL handshake, a client is expected to inspect the server-provided X.509 certificate and validate that the identity presented matches the hostname used to initiate the request. In the affected versions, the application neglects to perform this check, relying solely on the trust chain validation of the certificate authority (CA) without verifying the subject identity.\nThis omission creates a logical gap in the security stack, as any certificate signed by a trusted CA—regardless of the subject—will be accepted as legitimate for any destination host.\nThe attack flow proceeds as follows: First, the attacker positions themselves as a Man-in-the-Middle (MitM) through techniques such as ARP poisoning, DNS cache poisoning, or by compromising a router in the network path. Second, when the IntelliJ IDEA client attempts to communicate with a remote server (e.g., an update server, version control repository, or plugin marketplace), the attacker intercepts the connection request.\nThird, the attacker presents a valid, CA-signed certificate for a different domain under their control. Because the client fails to perform hostname verification, it fails to notice the discrepancy between the expected domain and the identity within the certificate.\nFinally, the handshake completes, and an encrypted tunnel is established between the client and the attacker’s machine. The attacker can then decrypt, inspect, and potentially modify the traffic before re-encrypting it and forwarding it to the actual server, effectively stripping away the confidentiality and integrity guarantees provided by TLS.\nThis vulnerability persists across all network-facing components of the IntelliJ IDEA platform that utilize the flawed TLS implementation. There are no authentication requirements for an attacker to initiate this interception, as the vulnerability resides in the transport layer negotiation process, which occurs prior to any application-level authentication. The exposure is limited to network-accessible segments where traffic interception is viable."
}