CVE-2026-78953 in Chrome
Summary
by MITRE • 08/25/2026
Missing authorization in SiteIsolation in Google Chrome prior to 152.0.7977.65 allowed a remote attacker who had compromised the renderer process to bypass site isolation via a crafted PDF file. (Chromium security severity: Medium)
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Analysis
by VulDB Data Team • 08/25/2026
The vulnerability identified as missing authorization within the SiteIsolation mechanism of Google Chrome prior to version 152.0.7977.65 represents a critical failure in browser-based process separation. Site Isolation is a fundamental security architecture designed to prevent cross-site scripting and data theft by ensuring that each site runs in its own unique operating system process. This isolation prevents malicious scripts from one origin from accessing sensitive data, such as cookies or local storage, belonging to another origin loaded within the same window or tab. The specific flaw involves an authorization gap where the renderer process, which is responsible for rendering web content and executing JavaScript, was not properly restricted in its ability to interact with other processes under certain conditions. This architectural weakness undermines the core promise of Site Isolation, effectively creating a bridge between isolated security contexts that should remain strictly separated.
The technical nature of this flaw centers on improper access control checks within the inter-process communication layer of the Chromium engine. When a renderer process is compromised by an attacker through malicious web content or scripts, it typically operates with limited privileges to prevent further system compromise. However, in this instance, the lack of rigorous authorization verification allowed the compromised renderer to bypass these restrictions. By exploiting this gap, an attacker could execute code that interacts directly with processes belonging to different sites, thereby breaking down the logical barriers intended to contain malicious activity within a single tab or window. This type of vulnerability is often categorized under CWE-269 Improper Privilege Management and relates closely to CWE-862 Missing Authorization, as it involves an actor performing actions without having been explicitly granted permission by the system's security policy.
The operational impact of this vulnerability is significant for users browsing untrusted or potentially malicious websites. A remote attacker who successfully compromises a renderer process via a crafted PDF file can escalate their privileges within the browser environment to access data from other tabs or windows that are open in the same Chrome instance. This could lead to session hijacking, where an attacker steals authentication tokens and cookies for banking sites, email accounts, or corporate portals. It also enables cross-site scripting attacks to become more potent by allowing script injection into contexts that were previously protected by process boundaries. The severity is rated as Medium because while it does not allow direct arbitrary code execution on the host operating system, it facilitates severe data exfiltration and privacy violations within the browser sandbox.
This vulnerability aligns with several tactics in the MITRE ATT&CK framework for enterprise security. Specifically, it relates to T1059 Command and Control using Browser Proxying or T1203 Exploitation for Client Execution if the renderer compromise leads to further payload delivery. More directly, it supports lateral movement within a user's browsing session by allowing access to other sites' data, which can be leveraged in conjunction with credential harvesting techniques found under T1556 Modification of Authentication Credentials. The use of a crafted PDF file as an attack vector highlights the importance of robust input validation and sandboxing for all content types processed by the browser, not just HTML pages.
Mitigation strategies primarily involve updating Google Chrome to version 152.0.7977.65 or later, where these authorization checks have been hardened. For organizations managing large fleets of devices, automated patch management systems should be configured to prioritize this update due to the active exploitation potential via common document formats like PDFs. Additionally, users can enhance their security posture by enabling strict Site Isolation policies through Chrome flags if available in their version and avoiding opening untrusted documents within tabs that contain sensitive sessions such as banking or administrative portals. Regularly auditing browser extensions is also recommended, as compromised extensions could potentially exploit similar isolation weaknesses to access data across different sites.