CVE-2021-30633: Google Chrome Use After Free Vulnerability

CVE-2021-30633 Overview

CVE-2021-30633 is a critical use-after-free vulnerability in the Indexed DB API of Google Chrome prior to version 93.0.4577.82. This memory corruption flaw allows a remote attacker who has already compromised the renderer process to potentially escape the browser's sandbox and execute arbitrary code on the underlying system. The vulnerability can be triggered through a specially crafted HTML page, making it exploitable via malicious websites or drive-by download attacks.

Critical Impact

This vulnerability has been actively exploited in the wild and is listed in CISA's Known Exploited Vulnerabilities Catalog. The sandbox escape capability makes this particularly dangerous as it allows attackers to break out of Chrome's security isolation and gain broader system access.

Affected Products

• Google Chrome versions prior to 93.0.4577.82
• Fedora Project Fedora 33
• Fedora Project Fedora 35

Discovery Timeline

• October 8, 2021 - CVE-2021-30633 published to NVD
• October 24, 2025 - Last updated in NVD database

Technical Details for CVE-2021-30633

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption vulnerability that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of Google Chrome's Indexed DB API, this flaw exists in how the browser handles database operations and object lifecycle management.

The Indexed DB API is a low-level JavaScript API for storing significant amounts of structured data in the browser. The use-after-free condition arises when database objects or transactions are freed prematurely while still being referenced elsewhere in the code. An attacker who has already achieved renderer process compromise can leverage this memory corruption primitive to manipulate freed memory, potentially achieving arbitrary read/write capabilities.

What makes this vulnerability particularly severe is the sandbox escape potential. Chrome's multi-process architecture isolates the renderer process from the rest of the system using a sandbox. By exploiting this use-after-free condition, an attacker can bypass these sandbox protections and execute code with the privileges of the browser process itself, significantly expanding the attack surface.

Root Cause

The root cause lies in improper object lifecycle management within the Indexed DB API implementation. When database objects are deallocated, references to these objects are not properly invalidated, creating dangling pointers. Subsequent operations that attempt to access these invalid references trigger the use-after-free condition.

The vulnerability specifically manifests in scenarios where asynchronous database operations interact with object cleanup routines, creating race conditions or timing windows that allow freed memory to be accessed before proper cleanup of all references.

Attack Vector

The attack requires a remote attacker to first compromise the Chrome renderer process through another vulnerability or attack vector. Once renderer compromise is achieved, the attacker can then deliver a crafted HTML page containing malicious JavaScript that triggers the use-after-free condition in the Indexed DB API.

The exploitation chain typically involves:

1. Initial renderer process compromise through a separate vulnerability
2. Delivery of a specially crafted HTML page to the victim
3. JavaScript execution that manipulates Indexed DB operations to trigger the use-after-free
4. Memory corruption exploitation to achieve arbitrary code execution outside the sandbox

The network-based attack vector combined with the requirement for user interaction (visiting a malicious page) makes this exploitable through phishing campaigns or compromised websites.

Detection Methods for CVE-2021-30633

Indicators of Compromise

• Unusual Chrome process behavior including unexpected child process spawning with elevated privileges
• Memory access violations or crashes within Chrome's Indexed DB components logged in system event logs
• Suspicious JavaScript execution patterns involving intensive Indexed DB API calls and object manipulation
• Evidence of sandbox escape attempts such as file system access or network connections from Chrome processes that should be sandboxed

Detection Strategies

• Monitor for Chrome versions below 93.0.4577.82 across enterprise endpoints using endpoint detection and response (EDR) solutions
• Implement browser-level telemetry to detect anomalous Indexed DB API usage patterns
• Deploy network monitoring to identify malicious HTML pages attempting to exploit this vulnerability through known exploit signatures
• Correlate Chrome crash reports with Indexed DB-related stack traces to identify potential exploitation attempts

Monitoring Recommendations

• Enable enhanced Chrome logging and forward logs to SIEM for analysis of renderer process anomalies
• Implement real-time endpoint monitoring for memory corruption indicators in browser processes
• Monitor for CISA KEV-related threat intelligence feeds to identify associated attack campaigns targeting this vulnerability
• Review web proxy logs for access to known malicious domains distributing exploit code

How to Mitigate CVE-2021-30633

Immediate Actions Required

• Upgrade Google Chrome to version 93.0.4577.82 or later immediately across all enterprise endpoints
• For Fedora systems, apply the security updates provided in the Fedora package announcements
• Enforce browser auto-update policies to prevent users from running vulnerable Chrome versions
• Consider temporarily restricting access to untrusted websites until patching is complete

Patch Information

Google has released a security update addressing this vulnerability in Chrome version 93.0.4577.82. The fix properly handles object lifecycle management in the Indexed DB API, ensuring that freed memory references are properly invalidated. For detailed information about the security update, refer to the Chrome Desktop Update Announcement.

Fedora users should apply the security updates available through the Fedora Package Announcements.

Given this vulnerability is listed in the CISA Known Exploited Vulnerabilities Catalog, organizations subject to CISA directives must prioritize remediation according to applicable deadlines.

Workarounds

• Deploy web filtering to block known malicious domains and URLs associated with exploitation attempts
• Implement network segmentation to limit the impact of potential sandbox escapes
• Enable Chrome's Site Isolation feature to provide additional renderer process isolation
• Consider deploying browser isolation solutions for high-risk users who may be targeted by sophisticated attacks

# Verify Chrome version on Linux/macOS
google-chrome --version
# Expected output: Google Chrome 93.0.4577.82 or higher

# Force Chrome update check on enterprise deployments
# Using Chrome Browser Cloud Management or Group Policy