CVE-2026-121248 in Chrome
Summary
by MITRE • 11/03/2026
Incorrect authorization in API in Google Chrome prior to 157.0.8103.38 allowed a remote attacker to bypass system access restrictions via a crafted Chrome extension. (Chromium security severity: Medium)
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Analysis
by VulDB Data Team • 11/03/2026
The vulnerability identified as an incorrect authorization issue within the application programming interface of Google Chrome, specifically affecting versions prior to 157.0.8103.38, represents a significant breach in access control mechanisms. This flaw allows remote attackers to circumvent system-level security restrictions by leveraging a maliciously crafted browser extension. The core technical deficiency lies in the improper validation of permissions and identity assertions when extensions interact with internal Chrome APIs. In a secure implementation, every request made by an extension must be rigorously authenticated and authorized against the user's granted privileges and the specific scope defined for that extension. However, due to this authorization bypass, the browser fails to adequately verify whether the requesting entity possesses the necessary rights to execute certain privileged operations or access sensitive data structures.
From a technical perspective, this vulnerability aligns with CWE-284, which describes Improper Access Control. The attacker exploits the lack of strict enforcement in the API layer by constructing an extension that mimics legitimate behavior while attempting to invoke functions reserved for higher-privilege contexts or internal browser processes. By sending crafted requests through these APIs, the malicious code can trigger actions that should be blocked under normal security policies. This could include accessing private user data such as browsing history, cookies, stored passwords, or interacting with other extensions and tabs in ways that violate cross-origin isolation principles. The severity is classified as medium because while it does not typically allow for direct remote code execution on the host operating system without further exploitation steps, it provides a foothold for deeper compromise by exposing sensitive user information or enabling session hijacking scenarios.
The operational impact of this vulnerability extends beyond simple data leakage. An attacker who successfully exploits this flaw can establish persistent access to the victim's browser environment. This capability facilitates surveillance activities where the attacker monitors web traffic, captures credentials entered into websites, and potentially manipulates page content for phishing attacks. Furthermore, because Chrome extensions often have broad permissions by design, bypassing authorization checks effectively grants the attacker a level of trust equivalent to that granted during installation. This undermines the fundamental security model of the browser, which relies on strict compartmentalization between different web contexts and extension sandboxes. The ability to bypass these restrictions erodes user confidence in the integrity of their browsing session and can lead to significant financial or reputational damage depending on the sensitivity of the accessed data.
In terms of threat modeling, this vulnerability maps closely to techniques found in the MITRE ATT&CK framework, particularly those related to Collection via Browser Extension and Privilege Escalation within a process context. Attackers may use this flaw as part of a larger campaign involving social engineering to trick users into installing malicious extensions that appear legitimate but contain code designed to exploit these API weaknesses. The exploitation does not require user interaction beyond the initial installation, making it particularly dangerous in enterprise environments where software deployment policies might be less stringent or where employees are targeted by sophisticated phishing campaigns.
To mitigate this risk, organizations and individual users must ensure that Google Chrome is updated to version 157.0.8103.38 or later immediately upon availability. This update contains the necessary patches to enforce stricter authorization checks within the API layer, ensuring that extensions cannot invoke privileged functions without explicit and verified permission grants. Additionally, administrators should review extension policies using enterprise management tools to restrict installation of unverified third-party extensions. Users are advised to audit installed extensions regularly, removing any that are no longer needed or exhibit suspicious behavior such as excessive resource usage or unexpected network activity. Implementing content security policies and leveraging browser hardening features can further reduce the attack surface by limiting the capabilities available to web content and extensions, thereby minimizing the potential impact even if a similar vulnerability were present in future versions.