CVE-2026-121183 in Chrome
Summary
by MITRE • 11/03/2026
Incorrect authorization in Extensions in Google Chrome prior to 157.0.8103.38 allowed a remote attacker who had compromised the renderer process to potentially execute arbitrary code outside the sandbox via a crafted HTML page. (Chromium security severity: Medium)
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Analysis
by VulDB Data Team • 11/03/2026
The vulnerability identified as an incorrect authorization flaw within Google Chrome's extension system prior to version 157.0.8103.38 represents a critical breach in the browser’s multi-process architecture, specifically targeting the boundary between renderer processes and higher-privilege components. This security severity issue is classified under CWE-269, which denotes Improper Control of Interaction with an External Entity, as it involves unauthorized escalation of privileges within the application's internal logic rather than a direct memory corruption error like buffer overflows or use-after-free conditions typically found in lower-level code execution flaws. The core technical flaw lies in the insufficient validation of permissions when extensions interact with specific browser APIs or internal interfaces that are intended to be restricted to privileged contexts, such as background pages or service workers.
In the Chromium architecture, renderer processes operate within a strict sandbox environment designed to limit their access to system resources and sensitive data. This isolation is fundamental to preventing remote code execution attacks from compromising the host operating system when rendering untrusted web content. However, this vulnerability allows an attacker who has already achieved arbitrary code execution or script injection within a compromised renderer process to bypass these restrictions. By crafting a specific HTML page that exploits the misconfigured authorization checks in extension APIs, the malicious payload can invoke functions or access resources that are normally reserved for trusted extensions with elevated privileges. This effectively breaks the sandbox boundary, allowing the attacker to execute commands outside the restricted environment where they were initially contained.
The operational impact of this vulnerability is significant because it transforms a relatively contained renderer compromise into a full system-level threat. An adversary leveraging this flaw can potentially install persistent malware, exfiltrate sensitive user data such as cookies and session tokens stored by extensions, or manipulate browser settings to redirect traffic through malicious proxies. Since the attack vector involves a crafted HTML page, it is highly feasible for attackers to distribute via phishing campaigns, compromised websites, or drive-by downloads that exploit other minor vulnerabilities in web content rendering. The ability to execute code outside the sandbox means that traditional defense-in-depth strategies relying on browser sandboxes are rendered ineffective against this specific exploitation path.
Mitigation efforts primarily involve upgrading Google Chrome and its underlying Chromium engine to version 157.0.8103.38 or later, where these authorization checks have been hardened to ensure strict adherence to the principle of least privilege for extension APIs. Security researchers map this type of vulnerability to MITRE ATT&CK technique T1204.002, User Execution: Malicious Link, as it often requires user interaction such as visiting a malicious site or clicking a link that triggers the crafted HTML payload. Additionally, administrators should enforce strict policies on which extensions are permitted within their environments and regularly audit extension permissions to minimize the attack surface available for privilege escalation attempts if similar flaws exist in other components of the browser ecosystem.