CVE-2026-121031 in Chrome
Summary
by MITRE • 11/03/2026
Missing authorization in PDF in Google Chrome prior to 157.0.8103.38 allowed a remote attacker to bypass web origin policy into a privileged page 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 missing authorization within the PDF handling component of Google Chrome prior to version 157.0.8103.38 represents a critical failure in access control mechanisms that governs how web origins interact with privileged internal pages. This flaw specifically affects the browser's ability to correctly validate permissions when processing Portable Document Format files through extensions or embedded viewers. The core technical issue lies in the insufficient separation of privileges between untrusted web content and higher-privileged browser interfaces, allowing a remote attacker to exploit this gap by crafting a malicious Chrome extension that manipulates PDF rendering contexts. By leveraging this misconfiguration, an adversary can bypass standard web origin policies which are designed to isolate different sources of information and prevent unauthorized access to sensitive data or functionality within the same-origin policy framework.
From a technical perspective, the vulnerability stems from a logic error in how the browser validates authorization tokens or permission checks when loading PDF documents via extension APIs. Normally, these mechanisms ensure that only authorized scripts or extensions can interact with privileged pages such as internal settings panels or secure document viewers. However, due to the missing check, an attacker-controlled extension could inject code into a context where it should not have access, effectively elevating its privileges beyond what is permitted by default security policies. This bypass allows the malicious entity to execute commands within a more trusted environment than intended, potentially leading to unauthorized data exfiltration or manipulation of browser state without user consent.
The operational impact of this vulnerability is significant as it undermines one of the foundational pillars of web security: origin isolation. When an attacker successfully exploits this flaw, they can access sensitive information stored in privileged pages that are typically shielded from standard web content. This could include cookies, local storage data, or internal browser configurations that contain user-specific details. Furthermore, because the attack vector involves a crafted Chrome extension, it may bypass certain sandboxing protections if the extension is granted broad permissions by the victim during installation. The severity rating of Medium reflects the balance between the complexity required to craft such an exploit and the potential for data compromise or further lateral movement within the browser environment once initial access is gained.
This incident aligns with common vulnerability classifications found in industry standards, particularly CWE-269 which denotes Improper Privilege Control, where a subject acts with elevated privileges without proper authorization. Additionally, it relates to ATT&CK technique T1059 Command and Scripting Interpreter if the exploit leads to arbitrary code execution within the browser process, or potentially T1537 Transfer Data to Cloud Account if data is exfiltrated via the compromised extension context. The exploitation scenario also touches upon aspects of cross-origin resource sharing misconfigurations when extensions interact with web content in unintended ways.
To mitigate this risk, users are strongly advised to update Google Chrome immediately to version 157.0.8103.38 or later where these authorization checks have been reinforced and validated against edge cases involving PDF rendering engines. Administrators should enforce strict policies on extension installation to prevent the deployment of unverified or overly permissive extensions that could serve as vectors for such attacks. Regular auditing of installed extensions and monitoring for unusual network activity originating from browser processes can also help in detecting potential exploitation attempts before significant damage occurs. Maintaining up-to-date software is the most effective defense against known vulnerabilities, ensuring that patches addressing these privilege escalation flaws are applied promptly to preserve the integrity of the browsing environment.