CVE-2026-87591 in Chrome
Summary
by MITRE • 09/09/2026
Incorrect authorization in Extensions in Google Chrome prior to 153.0.8010.36 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 • 09/09/2026
The vulnerability identified as an incorrect authorization flaw within the extensions subsystem of Google Chrome, specifically in versions prior to 153.0.8010.36, represents a significant breach in the browser's privilege separation model. This issue stems from a logic error where the application fails to properly validate whether a specific extension possesses the necessary permissions or authorization levels required to access certain system resources or execute privileged operations. In modern web browsers, extensions operate within a sandboxed environment with strictly defined capabilities granted via manifest declarations and user consent mechanisms. When this validation process is compromised, it allows an attacker who can influence or inject code into the browser context through a maliciously crafted extension to bypass these intended restrictions. The severity of this flaw is classified as medium by the Chromium security team, indicating that while exploitation requires specific conditions such as user interaction or installation of the rogue extension, the potential for unauthorized access and data exfiltration remains substantial.
From a technical perspective, the core deficiency lies in the authorization checks performed when an extension attempts to interact with sensitive APIs or system-level functions. Typically, browsers enforce strict boundaries between web content, extensions, and native applications to prevent cross-context attacks. However, this vulnerability suggests that the internal state management or permission verification logic did not correctly distinguish between authorized and unauthorized contexts for certain operations. An attacker could design a Chrome extension that appears benign on the surface but contains code designed to trigger these unchecked authorization paths. By leveraging specific API calls or event handlers that rely on implicit trust rather than explicit validation, the malicious extension can execute actions outside its declared scope. This effectively neutralizes the security model's intent to limit the blast radius of compromised extensions, allowing for broader system access than originally permitted by the user during installation.
The operational impact of this vulnerability is primarily centered around unauthorized data access and potential compromise of browser integrity. A remote attacker could exploit this flaw to read sensitive information stored within the extension's local storage or cookies that are typically protected from standard web page access. Furthermore, depending on the specific permissions granted by the user, such as access to browsing history, bookmarks, or network requests, the attacker could exfiltrate personal data, session tokens, or authentication credentials. In more severe scenarios involving extensions with elevated privileges like native messaging host connections, this flaw could facilitate lateral movement within a corporate environment or allow for persistent backdoor installation if combined with other vulnerabilities. The ability to bypass system access restrictions undermines user trust in the browser's security guarantees and exposes individuals and organizations to phishing, identity theft, and espionage activities facilitated by seemingly legitimate software components.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The primary defense is to update Google Chrome to version 153.0.8010.36 or later, where the authorization logic has been corrected to enforce strict permission checks before allowing extensions to perform sensitive operations. Organizations should implement automated patch management systems to ensure rapid deployment of security updates across all endpoints. Additionally, users and administrators should adopt a principle of least privilege by carefully reviewing extension permissions during installation, avoiding those that request excessive or unrelated access rights. Security monitoring tools can be configured to detect anomalous behavior from installed extensions, such as unexpected network connections or attempts to access restricted APIs. From a development standpoint, Chromium contributors must continue to enhance static analysis and fuzzing techniques targeting the extensions API surface area to identify similar logic flaws before they reach production releases.
This vulnerability aligns with common weakness enumeration categories related to authorization failures. Specifically, it corresponds to CWE-269 Improper Privilege Management, where a software product does not properly assign privileges or roles to actors in its environment. It also relates to CWE-862 Missing Authorization, as the extension was able to perform actions without being explicitly authorized for them. In terms of adversary tactics and techniques, this flaw facilitates behaviors associated with MITRE ATT&CK technique T1059 Command and Scripting Interpreter if used to execute further payloads, or T1074 Data Staged if data is collected locally before exfiltration. Understanding these mappings helps security teams prioritize detection rules and incident response procedures tailored to extension-based attacks. By addressing the root cause through code fixes and reinforcing user awareness regarding extension permissions, the risk of exploitation can be significantly reduced. Continuous vigilance and adherence to secure coding practices for browser extensions are essential to maintaining a robust defense against evolving threats that target these high-privilege components.