CVE-2026-6306: Google Chrome PDFium Buffer Overflow Flaw

CVE-2026-6306 Overview

A heap buffer overflow vulnerability exists in PDFium, the PDF rendering engine used by Google Chrome. This vulnerability affects versions of Google Chrome prior to 147.0.7727.101 and could allow a remote attacker to execute arbitrary code within the browser's sandbox by delivering a specially crafted PDF file. The vulnerability requires user interaction, as the victim must open or view a malicious PDF document.

Critical Impact

Remote attackers can achieve code execution within the Chrome sandbox through maliciously crafted PDF files, potentially compromising user systems if combined with additional sandbox escape vulnerabilities.

Affected Products

• Google Chrome versions prior to 147.0.7727.101
• Chromium-based browsers using vulnerable PDFium versions
• Applications embedding PDFium for PDF rendering

Discovery Timeline

• 2026-04-15 - CVE CVE-2026-6306 published to NVD
• 2026-04-16 - Last updated in NVD database

Technical Details for CVE-2026-6306

Vulnerability Analysis

This vulnerability is classified as CWE-122 (Heap-based Buffer Overflow). The flaw resides in PDFium, the open-source PDF rendering library integrated into Google Chrome for displaying PDF documents within the browser. When processing certain malformed PDF structures, PDFium fails to properly validate buffer boundaries during heap memory operations, allowing an attacker to write data beyond the allocated buffer.

The vulnerability can be triggered remotely through network-based attack vectors. An attacker could host a malicious PDF file on a website or deliver it via email, phishing campaigns, or other social engineering techniques. When a user opens the crafted PDF in an affected version of Chrome, the heap overflow condition is triggered.

While the code execution occurs within Chrome's sandbox, which provides some containment, heap overflow vulnerabilities of this nature can potentially be chained with sandbox escape techniques to achieve full system compromise. The requirement for user interaction (opening the PDF) provides some mitigation, but given the ubiquity of PDF documents in everyday workflows, the attack surface remains significant.

Root Cause

The root cause is a heap-based buffer overflow (CWE-122) in PDFium's PDF parsing and rendering code. The vulnerability stems from insufficient validation of data lengths or counts when allocating and writing to heap buffers during PDF document processing. Specifically, the parser does not adequately verify that input data fits within the allocated memory region before copying or processing it.

Attack Vector

The attack is network-based and requires user interaction. An attacker can exploit this vulnerability by:

1. Crafting a malicious PDF file containing specially structured elements that trigger the heap overflow
2. Distributing the PDF via web hosting, email attachments, or embedding in web pages
3. When a victim opens the PDF in Google Chrome (prior to version 147.0.7727.101), the malformed content causes PDFium to overflow a heap buffer
4. The attacker gains arbitrary code execution within the Chrome renderer sandbox

The vulnerability mechanism involves malformed PDF structures that cause PDFium to miscalculate buffer sizes during heap allocation. When subsequent data is written to this undersized buffer, it overflows into adjacent heap memory, potentially overwriting critical data structures or function pointers. For detailed technical analysis, refer to the Chromium Issue Tracker Entry.

Detection Methods for CVE-2026-6306

Indicators of Compromise

• Unexpected Chrome renderer process crashes when opening PDF files
• Suspicious PDF files with malformed internal structures or unusually large embedded objects
• Network traffic patterns showing downloads of PDF files from untrusted or newly registered domains
• Memory access violations or heap corruption errors in Chrome crash logs

Detection Strategies

• Monitor for Chrome crash reports specifically related to PDFium or PDF rendering operations
• Implement network-based detection for PDF files containing known malicious patterns or structural anomalies
• Deploy endpoint detection rules to identify suspicious process behavior following PDF file access
• Use sandboxing solutions to analyze PDF files before allowing user access

Monitoring Recommendations

• Enable Chrome's built-in crash reporting to capture potential exploitation attempts
• Monitor file system activity for PDF downloads from high-risk sources
• Track browser version deployments across the organization to identify unpatched instances
• Implement SIEM rules to correlate PDF access events with subsequent anomalous process activity

How to Mitigate CVE-2026-6306

Immediate Actions Required

• Update Google Chrome to version 147.0.7727.101 or later immediately
• Enable automatic Chrome updates to receive future security patches promptly
• Consider blocking PDF rendering in Chrome and using dedicated, isolated PDF readers until patching is complete
• Educate users about the risks of opening PDF files from untrusted sources

Patch Information

Google has released Chrome version 147.0.7727.101 which addresses this vulnerability. Organizations should prioritize updating all Chrome installations to this version or later. The official security advisory can be found at the Google Chrome Stable Update blog post. Enterprise environments using Chrome Enterprise should deploy the patched version through their management infrastructure.

Workarounds

• Disable Chrome's built-in PDF viewer and use external PDF applications with sandboxing capabilities
• Implement strict content filtering policies to scan and sanitize PDF files before delivery to end users
• Configure web proxies to block PDF downloads from untrusted domains
• Use browser isolation solutions to render potentially malicious content in isolated environments

# Chrome Enterprise policy to disable built-in PDF viewer (Windows Registry)
# Set this registry key to force Chrome to download PDFs instead of opening them
reg add "HKLM\SOFTWARE\Policies\Google\Chrome" /v AlwaysOpenPdfExternally /t REG_DWORD /d 1 /f

# Verify Chrome version via command line
google-chrome --version
# Ensure output shows 147.0.7727.101 or higher