CVE-2026-107938 in CXF
Summary
by MITRE • 10/09/2026
In Apache CXF, the Netty-based HTTP client transport (cxf-rt-transports-http-netty-client) did not verify that the hostname in the server’s TLS certificate matched the host being called. This applied over both HTTP/1.1 and HTTP/2, even when disableCNCheck was left at its default value of false. The certificate chain was validated against the configured trust store, but the endpoint’s identity was not. A network attacker able to intercept traffic could present any certificate trusted by the client, such as a publicly issued certificate for a domain they control, and impersonate the target service. They could then read or modify the exchanged messages, including credentials. Users are recommended to upgrade to versions 4.2.4 or 4.1.9 or 3.6.13, which fix this issue.
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Analysis
by VulDB Data Team • 10/09/2026
The vulnerability in Apache CXF’s Netty-based HTTP client transport represents a critical failure in the implementation of Transport Layer Security (TLS) hostname verification mechanisms. Specifically, within the cxf-rt-transports-http-netty-client module, the system fails to validate that the Common Name or Subject Alternative Names present in the server's TLS certificate correspond to the actual host address being accessed by the client application. This flaw persists regardless of whether the connection is established over HTTP/1.1 or HTTP/2 protocols and occurs even when the disableCNCheck configuration parameter remains at its default setting of false, indicating a fundamental logic error rather than a misconfiguration issue. While the certificate chain validation against the configured trust store proceeds correctly to ensure the authenticity of the Certificate Authority that issued the server's certificate, the subsequent step of verifying the identity of the endpoint itself is entirely bypassed. This omission breaks the core security guarantee provided by TLS, which is not only to encrypt data in transit but also to authenticate the remote party as the intended service.
From a technical perspective, this flaw allows for sophisticated man-in-the-middle attacks where an adversary positioned on the network path can intercept communications and present any valid certificate trusted by the client's trust store without restriction on domain matching. For instance, if the client trusts certificates issued by public Certificate Authorities, an attacker could obtain a legitimate-looking certificate for a different domain they control or exploit wildcard certificates to impersonate the target service. Because the client does not verify that the hostname in the URL matches the identity asserted in the certificate, it will accept this fraudulent connection as genuine. This effectively nullifies the security benefits of using HTTPS, reducing the protocol to mere encryption without authentication. The attacker can then decrypt, read, and potentially modify all exchanged messages with impunity, including sensitive credentials such as usernames, passwords, API keys, or session tokens transmitted during the interaction.
The operational impact of this vulnerability is severe, particularly for enterprise applications that rely on Apache CXF for web service communication over untrusted networks like the internet or compromised internal segments. An attacker leveraging this flaw can perform credential harvesting by capturing login details sent in plaintext after decryption, facilitate account takeover attacks, or inject malicious payloads into responses to compromise downstream systems. In environments where microservices communicate frequently and automatically, such a breach could lead to widespread data exfiltration or lateral movement within the network infrastructure. The risk is exacerbated because many developers assume that enabling TLS inherently provides full protection against interception, leading to complacency in security monitoring and incident response planning for these specific communication channels.
This vulnerability aligns with CWE-295 Improper Certificate Validation, specifically highlighting a failure to validate certificate hostname matching during the SSL/TLS handshake process. It also maps directly to MITRE ATT&CK technique T1078 Valid Accounts if used in conjunction with stolen credentials, or more broadly to network interception techniques where an attacker establishes themselves as a trusted intermediary. The lack of host verification is a classic implementation error that undermines the trust model established by Public Key Infrastructure standards such as RFC 5280 and X.509 certificate specifications which mandate strict identity binding between certificates and domain names.
To mitigate this risk, organizations must immediately upgrade Apache CXF to version 4.2.4, 4.1.9, or 3.6.13, depending on their current deployment baseline, as these releases contain the necessary code corrections to enforce proper hostname verification logic in the Netty client transport layer. In addition to upgrading software, security teams should audit existing configurations to ensure that no custom trust stores are overly permissive and consider implementing Certificate Pinning for high-value services where feasible. Regular vulnerability scanning of external-facing endpoints and internal service-to-service communications can help detect if any systems remain exposed or if anomalous certificate presentations occur during normal operations. Continuous monitoring for unusual TLS handshake patterns may also provide early warning indicators of exploitation attempts targeting this specific weakness in legacy deployments that have not yet been patched.