CVE-2026-75943 in EOS
Summary
by MITRE • 09/15/2026
A brief (milliseconds to seconds) traffic leak may occur when an authenticated supplicant is removed, either via the clear dot1x host all CLI command or due to a supplicant timeout. During this window, the supplicant's traffic may pass without ACL enforcement.
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Analysis
by VulDB Data Team • 09/15/2026
The vulnerability described involves a transient security gap in network access control mechanisms specifically within IEEE 802.1X authentication frameworks on networking infrastructure such as switches and wireless controllers. When an authenticated supplicant is removed from the system, either through explicit administrative action using commands like clear dot1x host all or due to automatic session termination caused by timeout events, there exists a brief interval where network traffic associated with that endpoint continues to traverse the device without being subjected to standard Access Control List enforcement. This window typically lasts for milliseconds to seconds but represents a significant deviation from the intended security posture which dictates that unauthorized or de-authenticated entities should be immediately blocked at Layer 2 or Layer 3 boundaries depending on implementation details.
From a technical perspective, this flaw stems from asynchronous state management within the authentication subsystem and the forwarding plane of the network device. The control plane processes the removal request and updates its internal database to reflect that the supplicant is no longer authorized, but there is often a delay before the data plane receives the updated policy instructions or flushes existing flow entries associated with that specific MAC address or IP identity. During this synchronization gap, packets belonging to the previously authenticated session are still permitted through based on stale forwarding state information rather than current authorization status. This behavior indicates an insufficiently tight coupling between authentication decisions and packet filtering actions, allowing traffic to bypass security policies during state transitions.
The operational impact of this vulnerability is primarily related to unauthorized data exfiltration or lateral movement within a segmented network environment. An attacker who has compromised the supplicant device could potentially exploit this brief window to transmit sensitive information before being disconnected from the network. Alternatively, if an attacker can trigger repeated authentication timeouts and removals, they might attempt to maintain persistent connectivity by repeatedly re-authenticating while exploiting these micro-windows of opportunity. In high-security environments where strict zero-trust principles are applied, even a millisecond-long bypass of ACL rules is unacceptable as it undermines the integrity of network segmentation strategies designed to contain threats within specific zones.
This issue aligns with CWE-284 Improper Access Control and CWE-367 Time-of-check Time-of-use (TOCTOU) Race Conditions in security contexts where state changes are not atomic relative to packet processing decisions. It also maps to MITRE ATT&CK techniques involving unauthorized access or privilege escalation through exploitation of timing vulnerabilities, specifically relating to how authentication states are enforced during session teardown phases. The vulnerability highlights the importance of implementing immediate flow invalidation mechanisms and ensuring that policy enforcement points operate synchronously with authentication state changes to eliminate any temporal gaps where security controls can be bypassed.
Mitigation strategies should focus on reducing or eliminating this time window through architectural improvements in network device firmware and configuration practices. Vendors typically address such issues by optimizing the synchronization between the control plane and data plane, ensuring that ACL updates are pushed immediately upon authentication state changes rather than waiting for periodic refresh cycles. Administrators can mitigate risk by implementing additional layers of security such as dynamic VLAN assignment with immediate reversion to a guest or quarantine VLAN upon disconnection, deploying intrusion detection systems that monitor for anomalous traffic patterns during session teardowns, and ensuring that all network devices are running the latest firmware versions provided by vendors which include patches for these synchronization flaws. Regular auditing of authentication logs can also help detect unusual patterns of rapid disconnect-reconnect cycles that might indicate exploitation attempts targeting this specific timing vulnerability.