CVE-2026-121166 in Chrome
Summary
by MITRE • 11/03/2026
Type confusion in PDFium in Google Chrome prior to 157.0.8103.38 allowed a remote attacker to execute arbitrary code inside the sandbox via a crafted PDF file. (Chromium security severity: High)
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified as a type confusion flaw within PDFium, the core rendering engine used by Google Chrome prior to version 157.0.8103.38, represents a critical memory safety issue that allows for arbitrary code execution under specific conditions. Type confusion vulnerabilities occur when an application incorrectly interprets data of one type as another, leading to undefined behavior during runtime operations. In the context of PDFium, this misinterpretation typically arises from improper handling of object references or internal structures within complex PDF documents. When a remote attacker crafts a malicious PDF file containing specifically designed objects with mismatched types, they can trick the renderer into performing memory operations on data that does not match its expected structure. This discrepancy often results in heap corruption, such as out-of-bounds writes or use-after-free scenarios, which are foundational prerequisites for achieving arbitrary code execution.
The operational impact of this vulnerability is severe due to the sandboxing architecture employed by modern web browsers like Chrome. While browser sandboxes are designed to restrict untrusted content from accessing sensitive system resources, they do not provide absolute isolation against all memory corruption exploits. By leveraging a type confusion flaw within PDFium, an attacker can manipulate internal pointers or function tables to bypass these security boundaries. Once the sandbox is breached through precise heap exploitation techniques, the malicious code executes with the privileges of the browser process rather than being confined to a restricted environment. This capability enables the remote execution of arbitrary commands on the victim's machine, potentially leading to full system compromise if further privilege escalation vectors are available or if sensitive data stored within the browser profile is accessed directly.
From a classification perspective, this vulnerability aligns with CWE-843, which describes access to incorrect type via reference, and often involves elements of CWE-120, buffer copy without checking size limits, depending on how the memory corruption manifests during exploitation. In terms of offensive security frameworks such as MITRE ATT&CK, this exploit technique falls under T1205.008, specifically Weak or Untrusted Code in Third Party Application Components, and facilitates initial access through drive-by compromise mechanisms where users are tricked into opening malicious documents. The high severity rating assigned by the Chromium team reflects both the complexity of exploitation required to achieve code execution and the widespread exposure given PDFium's integration across multiple platforms including Windows, macOS, Linux, Android, and iOS.
Mitigation strategies primarily involve immediate patching to version 157.0.8103.38 or later, which includes fixes for the underlying memory management logic in PDFium that prevents type misinterpretation during document parsing. Organizations should enforce strict policies regarding the opening of untrusted PDF files and consider deploying browser hardening techniques such as disabling JavaScript execution in embedded viewers where possible. Additionally, implementing network-level controls to filter out suspicious file types or scanning incoming documents with advanced threat protection solutions can reduce exposure to crafted payloads designed to trigger this specific memory corruption flaw before it reaches end-user devices.