CVE-2026-121243 in Chrome
Summary
by MITRE • 11/03/2026
Information leak in Frames in Google Chrome prior to 157.0.8103.38 allowed a remote attacker to obtain sensitive information via a crafted HTML page. (Chromium security severity: Low)
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Analysis
by VulDB Data Team • 11/03/2026
The vulnerability identified as an information leak within the frame handling mechanisms of Google Chrome versions prior to 157.0.8103.38 represents a significant breach in browser isolation principles. This flaw specifically affects how the browser manages cross-origin frames, which are essential for embedding content from different sources into a web page while maintaining security boundaries. The core technical issue lies in the improper handling of context separation between these embedded frames and their parent containers or other sibling frames. When an attacker constructs a malicious HTML page designed to exploit this specific logic error, they can bypass intended restrictions that prevent unauthorized access to data residing within isolated frame contexts. This failure allows the crafted script running within one frame to read sensitive information from another frame where it should have no visibility, effectively breaking the same-origin policy protections that are fundamental to modern web security architectures.
From a technical perspective, this vulnerability is categorized under CWE-200, which defines an Information Exposure issue where software leaks information through its output or behavior in ways not intended by developers. The exploitation vector relies on social engineering combined with precise code execution within the browser environment. An attacker hosts a specially crafted HTML page that utilizes JavaScript to interact with frame elements across different origins. Due to the flaw in Chrome's rendering engine, specifically within the Blink component responsible for layout and DOM manipulation, the security checks validating access permissions are either skipped or incorrectly evaluated. This allows the malicious script to retrieve data such as cookies, local storage contents, or sensitive form inputs from a victim site that has been loaded into an iframe on the attacker’s page. The severity is rated as low by Chromium standards because it typically requires user interaction and specific browser configurations to be fully exploitable in many real-world scenarios, yet it remains dangerous for high-value targets where session hijacking or credential theft via cross-frame scripting could lead to account compromise.
The operational impact of this vulnerability centers on the potential for unauthorized data exfiltration without direct access to the victim’s machine. By leveraging this flaw, a remote attacker can perform sophisticated phishing attacks that go beyond simple deception by actively harvesting sensitive information from authenticated sessions. For instance, if a user is logged into an email service or financial portal within one frame of a malicious page, and another frame loads a different site with its own data structures, the vulnerability could allow the attacker to read details from either context depending on how the frames are structured and accessed. This undermines trust in web applications that rely heavily on iframe integration for features like single sign-on or embedded widgets. The attack aligns with MITRE ATT&CK technique T1059, specifically sub-techniques related to command and script interpreters such as JavaScript, which attackers use to automate the extraction of data from browser memory after gaining initial execution privileges through a crafted webpage.
Mitigation for this vulnerability primarily involves updating Google Chrome to version 157.0.8103.38 or later, where these frame isolation checks have been hardened and validated against cross-origin access attempts. For organizations unable to patch immediately due to compatibility constraints, deploying browser security policies that restrict the use of iframes on untrusted domains can provide a layer of defense in depth. Additionally, implementing Content Security Policy headers with strict directives regarding frame ancestors and sandbox attributes helps limit the scope of what embedded content can do, reducing the attack surface even if the underlying engine flaw persists. Developers should also audit their own applications for improper use of cross-origin messaging APIs like postMessage, ensuring that origin checks are rigorously performed before processing incoming data from frames to prevent secondary exploitation vectors stemming from this class of vulnerability.