CVE-2026-121615 in E5600
Summary
by MITRE • 11/04/2026
A vulnerability was determined in Linksys E5600 1.1.0.26. Affected is an unknown function of the file /cgi-bin/mesh_login.cgi of the component Login Handler. Executing a manipulation can lead to improper authentication. The attack can be launched remotely. The exploit has been publicly disclosed and may be utilized. The vendor was contacted early about this disclosure but did not respond in any way. This vulnerability only affects products that are no longer supported by the maintainer.
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Analysis
by VulDB Data Team • 11/04/2026
The Linksys E5600 router, specifically running firmware version 1.1.0.26, contains a critical authentication bypass flaw within its mesh networking login handler component. The vulnerability resides in an unknown function of the /cgi-bin/mesh_login.cgi script, which is responsible for managing user credentials and session validation for Mesh Wi-Fi features. This specific implementation error allows attackers to manipulate input parameters or request structures to circumvent standard authentication mechanisms. By exploiting this flaw, a remote attacker can gain unauthorized access to the administrative interface without valid credentials, effectively bypassing security controls designed to protect device configuration and network settings.
From a technical perspective, this vulnerability is classified under CWE-287, which denotes Improper Authentication. The root cause likely involves insufficient validation of authentication tokens or session identifiers within the CGI script logic. When an attacker sends a specially crafted HTTP request to the mesh_login.cgi endpoint, the server fails to verify the legitimacy of the provided credentials or session state properly. This failure results in the system granting access as if the user had successfully authenticated through normal channels. The remote nature of this exploit means that no physical proximity or local network access is required beyond standard internet connectivity, significantly increasing the attack surface and risk profile for deployed devices.
The operational impact of this vulnerability is severe due to the privileged level typically associated with router administrative interfaces. An attacker who exploits this flaw can modify DNS settings, redirect traffic through malicious proxies, open ports for further intrusion, or install persistent malware on the device. This compromises not only the individual user but potentially all devices connected to that network. The situation is exacerbated by the fact that exploit code has been publicly disclosed and may be utilized by threat actors in automated attacks. Furthermore, Linksys did not respond to early notifications regarding this disclosure, leaving users without official patches or guidance for remediation.
This vulnerability aligns with MITRE ATT&CK technique T1078, Valid Accounts, as it allows an adversary to establish persistence using legitimate-looking credentials obtained through bypass rather than theft. Additionally, the lack of vendor support places these devices in a high-risk category where traditional mitigation strategies like patching are unavailable. Organizations and individuals relying on this hardware must consider immediate decommissioning or network segmentation to isolate vulnerable units from critical infrastructure. Since no fix is forthcoming, reliance on external security controls such as intrusion detection systems configured to detect exploitation attempts of the mesh_login.cgi endpoint becomes essential for maintaining baseline security posture until replacement with supported hardware occurs.