CVE-2026-121239 in Chrome
Summary
by MITRE • 11/03/2026
Information leak in Core in Google Chrome prior to 157.0.8103.38 allowed a remote attacker to obtain cross-origin data 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 information leak within the core components of Google Chrome, specifically affecting versions prior to 157.0.8103.38, represents a significant breach in browser isolation mechanisms. This flaw allows a remote attacker to access cross-origin data that should remain strictly segregated from other browsing contexts. The issue stems from an improper handling of memory or state within the Chromium engine's core processing logic, where safeguards designed to enforce same-origin policy are bypassed through specific manipulation techniques. By crafting a malicious HTML page that exploits this weakness, an adversary can trick a victim into loading content that triggers the vulnerability, thereby gaining unauthorized access to sensitive information stored in other tabs or windows belonging to different origins.
From a technical perspective, this flaw aligns with CWE-200, which categorizes issues related to exposure of sensitive information to an unauthorized actor. The attack vector relies on social engineering combined with precise code execution within the browser environment. When a user visits the crafted webpage, the malicious script interacts with the DOM or internal APIs in a way that circumvents standard security checks. This could involve accessing cookies, local storage data, or form inputs from other sites if they are open in the same browser instance and share certain characteristics exploited by the bug. The severity is rated as medium because while it does not allow for arbitrary code execution on the host system, it compromises user privacy and can facilitate further attacks such as session hijacking or credential theft if sensitive data like authentication tokens are exposed.
The operational impact of this vulnerability extends beyond simple data leakage. It undermines the fundamental trust model of web browsers, which rely heavily on strict isolation between different websites to prevent cross-site scripting and other related attacks. If an attacker can read cross-origin data, they may be able to correlate user activities across multiple sites or steal session identifiers that grant access to protected resources. This capability is particularly dangerous in environments where users frequently log into sensitive accounts such as banking portals, email services, or corporate intranets while browsing less secure websites. The exploitation does not require elevated privileges on the victim's machine and can be triggered remotely via a link or embedded iframe, making it scalable for large-scale phishing campaigns.
In terms of threat intelligence frameworks, this vulnerability maps to MITRE ATT&CK techniques involving Collection from Browser or potentially Credential Access if session tokens are harvested. The attack pattern resembles aspects of Cross-Site Scripting (XSS) but focuses specifically on data exfiltration rather than code execution within the victim's context. Defenders and users must recognize that even medium-severity vulnerabilities in core browser components can have high-impact consequences depending on the sensitivity of the data accessed. It is crucial to understand that modern browsers employ multiple layers of defense, including sandboxing and site isolation, but bugs in these foundational systems can temporarily weaken those barriers until patches are applied.
To mitigate this risk, immediate action must be taken by updating Google Chrome to version 157.0.8103.38 or later across all endpoints within the organization. Automated patch management solutions should be configured to prioritize browser updates due to their widespread use and critical role in security posture. Additionally, users should enable automatic update notifications to ensure they are alerted when new versions become available. Security teams should also monitor for indicators of compromise that might suggest exploitation attempts, such as unusual network traffic patterns originating from the browser process or unexpected access logs on web applications where session tokens were potentially stolen. Implementing strict Content Security Policies and disabling unnecessary features like third-party cookies can further reduce the attack surface, although these measures are complementary rather than substitutes for timely patching. Regular security awareness training should also be conducted to help users identify suspicious links that might lead to pages designed to exploit such vulnerabilities.