CVE-2026-100665 in Netty
Summary
by MITRE • 09/26/2026
Netty versions from 4.2.11.Final before 4.2.18.Final contain an incomplete hostname verification fix in the QUIC certificate verification path when using a plain X509TrustManager. The BoringSSLCertificateVerifyCallback discards the SSLEngine for plain trust managers, preventing endpoint identification from running even when HTTPS verification is configured. Attackers on the network path can present a certificate chain for the wrong hostname that the plain trust manager accepts, bypassing hostname authentication for QUIC clients.
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Analysis
by VulDB Data Team • 09/26/2026
The vulnerability identified in Netty versions ranging from 4.2.11.Final up to but not including 4.2.18.Final represents a critical failure in transport layer security enforcement within the QUIC protocol implementation. This flaw specifically targets the certificate verification mechanism when developers utilize a plain X509TrustManager for handling SSL/TLS handshakes. In secure network communications, it is standard practice to verify not only that a server's certificate is signed by a trusted Certificate Authority but also that the hostname presented in the certificate matches the intended destination host. This process, known as endpoint identification or hostname verification, prevents man-in-the-middle attacks where an attacker might present a validly signed certificate for a different domain. The vulnerability arises because the internal callback responsible for verifying certificates, specifically BoringSSLCertificateVerifyCallback, incorrectly discards the SSLEngine context when it detects that a plain trust manager is being used. This premature disposal of the engine state effectively disables the subsequent hostname verification logic, even if HTTPS-style verification settings are explicitly configured by the application developer.
From an operational perspective, this defect allows attackers positioned on the network path to perform sophisticated man-in-the-middle attacks against QUIC clients using Netty. By presenting a certificate chain that is cryptographically valid and signed by a trusted authority but associated with a different hostname than the one being accessed, an attacker can successfully intercept encrypted traffic. Because the plain X509TrustManager accepts the certificate based solely on its signature validity without checking the subject alternative names or common name against the target host, the connection proceeds as if it were secure and authentic. This bypasses the fundamental security guarantee of TLS/QUIC, which is to ensure that the client is communicating with the intended server entity rather than an impersonator. The impact is severe for applications relying on QUIC for low-latency communication, such as streaming services or real-time data exchanges, as sensitive data transmitted over these connections can be intercepted and potentially modified without detection by the application layer.
This vulnerability aligns closely with CWE-295 Improper Certificate Validation, specifically the sub-category of failing to validate certificate hostnames. It also maps to MITRE ATT&CK technique T1078 Valid Accounts or more broadly to network-based interception techniques where an attacker exploits trust relationships established during handshake negotiations. The root cause lies in a logic error within the BoringSSL integration layer that prioritizes compatibility with plain trust managers over security completeness, inadvertently stripping away essential identity verification steps. To mitigate this risk, organizations running affected versions of Netty must upgrade to version 4.2.18.Final or later where the hostname verification path has been corrected to ensure it runs regardless of the trust manager type used. Until an upgrade is feasible, developers should consider implementing custom SSLContext configurations that enforce strict hostname verification explicitly before initiating QUIC connections, although upgrading remains the only definitive resolution for this code-level defect in the library itself.