CVE-2026-106263 in Chrome
Summary
by MITRE • 10/06/2026
Improper input validation in SignIn in Google Chrome prior to 155.0.8059.39 allowed a remote attacker leveraging social engineering to bypass system access restrictions via a crafted Chrome extension. (Chromium security severity: Medium)
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Analysis
by VulDB Data Team • 10/07/2026
The vulnerability identified as an improper input validation flaw within the SignIn component of Google Chrome prior to version 155.0.8059.39 represents a significant risk vector for unauthorized access and privilege escalation through malicious browser extensions. This issue stems from insufficient sanitization or verification mechanisms applied to inputs processed during the authentication workflow, specifically when interacting with extension APIs that request permissions or manage user sessions. By exploiting this deficiency, an attacker can craft a deceptive Chrome extension designed to trick users into granting elevated privileges or bypassing existing security restrictions. The core technical flaw lies in the application's failure to rigorously validate the structure and intent of data passed through the SignIn interface, allowing malformed or specially constructed payloads to manipulate internal state variables that control access levels.
From an operational perspective, this vulnerability relies heavily on social engineering tactics to achieve its objectives. Unlike remote code execution vulnerabilities that can be triggered by simply visiting a malicious website, this exploit requires user interaction and consent. An attacker would distribute the crafted extension through unofficial channels or disguise it as legitimate software within the Chrome Web Store before it is detected and removed. Once installed, the extension leverages the input validation gap to bypass system access restrictions, potentially gaining unauthorized control over sensitive browser data, session cookies, or authentication tokens. This capability effectively neutralizes several layers of defense that rely on user consent for permission grants, as the malicious code manipulates the expected flow of the SignIn process to appear legitimate while executing hidden actions in the background.
The security severity is classified as Medium by Chromium standards because, although it allows for significant access bypasses, it does not provide direct remote code execution without user involvement. However, the impact on confidentiality and integrity remains high if successful exploitation occurs. Attackers can use this method to steal credentials, maintain persistent access through hijacked sessions, or install additional malware under the guise of a trusted application. This aligns with CWE-20 Improper Input Validation, where the software does not sufficiently verify that input meets specified requirements before processing it. Furthermore, the attack vector corresponds to MITRE ATT&CK techniques related to Initial Access via Trusted Software Distribution and Privilege Escalation through Browser Extension APIs, highlighting the importance of securing extension permission models against manipulation.
Mitigation strategies primarily involve updating Google Chrome to version 155.0.8059.39 or later, where these input validation checks have been strengthened to reject malformed requests during the SignIn process. Users should exercise caution when installing extensions from unknown sources and review requested permissions carefully before granting access. Security administrators can also enforce policies that restrict extension installation to approved lists within enterprise environments, reducing the attack surface available for social engineering campaigns. Continuous monitoring of browser behavior and logging unusual permission grant patterns can further aid in detecting attempts to exploit this vulnerability before significant damage occurs.