CVE-2026-116541 in tcnative
Summary
by MITRE • 10/26/2026
Netty netty-tcnative before 2.0.84.Final contains a denial of service vulnerability in the tcn_write_to_bytebuffer BIO write callback that overreports bytes consumed. Remote TLS 1.3 peers can provoke queued post-handshake records like NewSessionTicket or KeyUpdate to truncate flights, fail connections, or abort the JVM process.
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Analysis
by VulDB Data Team • 10/26/2026
The Netty project is a widely adopted asynchronous event-driven network application framework for Java that provides high-performance networking capabilities through its native transport components. Within this ecosystem, netty-tcnative serves as a wrapper around OpenSSL and other TLS libraries to enable efficient SSL/TLS handling in non-blocking environments. A critical flaw was identified in versions prior to 2.0.84.Final specifically within the tcn_write_to_bytebuffer BIO write callback mechanism. This component is responsible for managing how data flows from the application layer into the underlying transport buffer during TLS operations. The vulnerability stems from an incorrect accounting of bytes consumed during this process, leading to a state mismatch between what OpenSSL believes has been processed and what Netty actually acknowledges as handled.
This technical flaw manifests primarily when interacting with remote peers using TLS 1.3 protocols. In TLS 1.3, post-handshake messages such as NewSessionTicket or KeyUpdate are transmitted independently of the initial handshake sequence to maintain session state and cryptographic key rotation without interrupting ongoing connections. When these specific records are processed through the flawed callback, the system overreports the number of bytes consumed from the input buffer. This discrepancy causes the internal flow control logic to incorrectly assume that more data has been successfully written or acknowledged than is actually true. Consequently, subsequent flight packets may be truncated prematurely because the framework believes it has already sent sufficient data, leading to incomplete message transmission and protocol state desynchronization.
The operational impact of this vulnerability is severe, primarily resulting in denial-of-service conditions for both client and server endpoints. Affected systems can experience abrupt connection failures where established TLS sessions are terminated unexpectedly due to the malformed or truncated packet flights. In more extreme scenarios, particularly when dealing with crafted malicious inputs designed to exploit the buffer state inconsistency, the error propagation can lead to a Java Virtual Machine crash. This effectively results in a complete service outage for any application relying on netty-tcnative for its TLS termination or initiation needs, as the JVM process aborts rather than gracefully handling the protocol violation.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-400 Resource Exhaustion due to incorrect resource accounting in network protocols. It also maps to MITRE ATT&CK technique T1499 Endpoint Denial of Service, specifically under subcategories involving application exhaustion or protocol abuse. The attack vector is remote, requiring only a network connection with TLS 1.3 support and the ability to send specific post-handshake messages that trigger the buggy callback path. There are no known workarounds for this issue other than upgrading the library version, as the flaw resides in core logic governing byte buffer management which cannot be easily bypassed via configuration changes.
To mitigate this risk, organizations utilizing Netty must upgrade netty-tcnative to version 2.0.84.Final or later immediately upon availability. This update contains patches that correct the byte consumption reporting logic within the tcn_write_to_bytebuffer callback, ensuring accurate state tracking during TLS post-handshake operations. Additionally, security teams should monitor for unusual connection drops or JVM crashes in environments running older versions of Netty with TLS 1.3 enabled. Implementing network-level rate limiting on new connections can provide a temporary layer of defense against automated exploitation attempts while patch management is being executed across the infrastructure.