CVE-2026-106421 in Chrome
Summary
by MITRE • 10/07/2026
Use after free in PDF in Google Chrome prior to 155.0.8059.39 allowed a remote attacker to execute arbitrary code inside the sandbox via a crafted HTML page. (Chromium security severity: High)
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Analysis
by VulDB Data Team • 10/07/2026
The vulnerability described constitutes a critical memory safety issue within the PDF rendering engine of Google Chrome, specifically affecting versions prior to 155.0.8059.39. This flaw is classified as an out-of-bounds use or use-after-free condition, which represents one of the most dangerous categories of software defects in modern application development. The root cause lies in improper management of memory pointers within the PDF processing module. When Chrome parses a maliciously crafted HTML page that embeds or references a specially constructed PDF document, it allocates specific data structures to handle the rendering and interpretation of the file contents. However, due to a logic error in the reference counting or lifecycle management of these objects, the application may release or free the memory associated with certain internal pointers while they are still being actively referenced by other parts of the execution context. This creates a dangling pointer scenario where subsequent operations attempt to access memory that has already been deallocated and potentially reallocated for different purposes.
From a technical perspective, this vulnerability aligns closely with Common Weakness Enumeration identifier CWE-416, which defines use after free as accessing or using pointers after their associated storage is freed. The exploitation of such flaws typically relies on the attacker's ability to control the contents of the newly allocated memory that replaces the freed block. By carefully crafting the PDF file and the surrounding HTML context, an adversary can manipulate heap allocation patterns to ensure that sensitive data structures are overwritten with controlled values. This manipulation allows the attacker to hijack program flow or corrupt internal state in a way that facilitates arbitrary code execution. The severity is rated as High by Chromium security standards because it bypasses standard memory safety protections and provides a direct path to executing malicious payloads within the browser's process space.
The operational impact of this vulnerability is severe, particularly given its potential for remote exploitation via a crafted HTML page. An attacker does not need physical access or user interaction beyond visiting a compromised website or being tricked into opening an email with a linked PDF viewer embedded in HTML. Once triggered, the use-after-free condition can lead to arbitrary code execution inside the browser sandbox. While Chrome employs robust sandboxing mechanisms designed to limit the damage of such exploits by restricting file system and network access for renderer processes, successful exploitation still poses significant risks. It can allow attackers to escalate privileges within the sandboxed environment, exfiltrate sensitive data stored in cookies or local storage, install persistent malware, or use the compromised browser as a pivot point for further attacks against the host operating system if additional vulnerabilities are chained together.
Mitigation strategies primarily involve immediate software updates and defensive coding practices. The most effective remediation is to upgrade Google Chrome to version 155.0.8059.39 or later, where this memory management flaw has been corrected by ensuring proper reference counting and preventing access to freed memory blocks. For organizations unable to patch immediately, deploying browser isolation technologies or content security policies that restrict the embedding of PDFs in HTML contexts can reduce exposure. Furthermore, developers should adhere to secure coding standards such as those outlined in OWASP guidelines for input validation and resource management. Implementing static analysis tools during the development lifecycle can help detect potential use-after-free conditions before deployment. Additionally, enabling advanced sandboxing features and keeping operating system-level protections like ASLR and DEP enabled provides essential layers of defense that complicate exploitation attempts even if a vulnerability is present.
This incident highlights the ongoing challenges in maintaining memory safety within complex web browsers. The ATT&CK framework categorizes such exploits under techniques involving initial access through spearphishing links or drive-by downloads, followed by execution via browser-based code injection. Understanding these patterns helps security teams prioritize monitoring for indicators of compromise related to unusual PDF processing activity and anomalous network connections originating from the Chrome process. Continuous vigilance and rapid patching cycles remain critical in defending against high-severity vulnerabilities that target core components like rendering engines.