CVE-2026-114641 in Traefik
Summary
by MITRE • 10/22/2026
Traefik 2.11.x before 2.11.58 and 3.x before 3.7.14 contains a race condition in NTLM and Kerberos (Negotiate) backend authentication, where the per-connection sticky round tripper slot is read and written without synchronization. Remote attackers can send concurrent HTTP/2 or HTTP/3 requests over one connection to orphan backend connections, break connection-bound authentication, or crash Traefik.
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Analysis
by VulDB Data Team • 10/22/2026
The vulnerability identified in Traefik versions 2.11.x prior to 2.11.58 and version 3.x prior to 3.7.14 represents a critical race condition within the backend authentication mechanism for NTLM and Kerberos protocols, specifically under the Negotiate scheme. This flaw stems from improper synchronization of shared state during concurrent request processing over HTTP/2 or HTTP/3 connections. In these modern multiplexed protocol implementations, multiple logical streams are transmitted simultaneously over a single TCP connection. The Traefik proxy utilizes per-connection sticky round tripper slots to manage authentication contexts and backend connection pooling for these specific protocols. However, the code fails to implement adequate locking mechanisms when reading from or writing to these shared slot structures. This lack of synchronization creates a classic time-of-check-to-time-of-use scenario where concurrent threads can interfere with each other's operations on the same memory location, leading to unpredictable behavior and state corruption.
From an operational perspective, this race condition allows remote attackers who have access to the Traefik entry point to exploit the concurrency flaw by sending multiple simultaneous requests over a single HTTP/2 or HTTP/3 connection. The primary impact involves the orphaning of backend connections, which occurs when the authentication context is incorrectly associated with a different request stream due to the race condition. This breaks connection-bound authentication guarantees, potentially allowing an attacker to bypass access controls intended for specific users or services by hijacking the authentication state established by another concurrent request. Furthermore, the corruption of internal data structures can lead to severe stability issues, including segmentation faults and process crashes, resulting in a denial of service against the reverse proxy infrastructure. This undermines both the confidentiality and availability aspects of the system's security posture.
The technical classification of this vulnerability aligns with CWE-362, which describes concurrent execution using shared resources with inadequate synchronization. The exploitation technique involves manipulating HTTP/2 or HTTP/3 stream multiplexing to trigger simultaneous access to unprotected memory regions within the Traefik process. In terms of adversary tactics, this falls under ATT&CK T1078, Valid Accounts, as it allows for authentication bypass through state manipulation rather than credential theft. It also relates to ATT&CK T1499, Endpoint Denial of Service, due to the potential for causing application crashes via resource exhaustion or memory corruption triggered by the race condition. The vulnerability highlights a common pitfall in high-performance web proxies where performance optimizations involving connection reuse and multiplexing are not adequately paired with thread-safety guarantees for shared state variables.
Mitigation strategies primarily involve upgrading Traefik to version 2.11.58 or later, or version 3.7.14 and above, which include the necessary synchronization fixes in the authentication backend logic. Until an upgrade is feasible, organizations should consider implementing rate limiting on entry points that handle NTLM or Kerberos authentication to reduce the likelihood of concurrent requests hitting the vulnerable code path simultaneously. Additionally, deploying a Web Application Firewall with rules designed to detect anomalous patterns of HTTP/2 stream creation may provide some level of compensating control by mitigating the ability to trigger the race condition at scale. It is also advisable to review network segmentation policies to ensure that only trusted clients can access services relying on these specific authentication methods, thereby reducing the attack surface available for exploitation.