CVE-2021-21124
📋 TL;DR
This is a use-after-free vulnerability in Google Chrome's Speech Recognizer component on Android. It allows a remote attacker to potentially escape Chrome's sandbox and execute arbitrary code by tricking a user into visiting a malicious webpage. Only affects Chrome on Android versions before 88.0.4324.96.
💻 Affected Systems
- Google Chrome
📦 What is this software?
Chrome by Google
Google Chrome is the world's most popular web browser, used by over 3 billion users globally across Windows, macOS, Linux, Android, and iOS platforms. As a Chromium-based browser developed by Google, Chrome dominates the browser market with approximately 65% market share, making it a critical compon...
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⚠️ Risk & Real-World Impact
Worst Case
Full device compromise - attacker escapes Chrome sandbox, gains arbitrary code execution with user privileges, potentially leading to data theft, ransomware, or persistent access.
Likely Case
Limited sandbox escape leading to data exfiltration from Chrome or installation of additional malware, but full device compromise requires chaining with other vulnerabilities.
If Mitigated
Attack fails or only causes Chrome crash if sandbox escape is prevented by OS-level protections or if exploit is incomplete.
🎯 Exploit Status
Exploit requires user to visit crafted HTML page. No public exploit code available, but vulnerability was actively exploited according to some reports.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 88.0.4324.96 and later
Vendor Advisory: https://chromereleases.googleblog.com/2021/01/stable-channel-update-for-desktop_19.html
Restart Required: Yes
Instructions:
1. Open Google Play Store on Android device. 2. Search for 'Chrome'. 3. If update available, tap 'Update'. 4. After update completes, restart Chrome.
🔧 Temporary Workarounds
Disable Speech Recognition
androidTemporarily disable Chrome's speech recognition feature to remove attack surface.
chrome://settings/content/speech
Use Alternative Browser
androidSwitch to a different browser until Chrome is updated.
🧯 If You Can't Patch
- Restrict access to untrusted websites using network filtering or DNS blocking.
- Implement application whitelisting to prevent execution of unknown binaries if sandbox escape occurs.
🔍 How to Verify
Check if Vulnerable:
Open Chrome on Android, go to Settings > About Chrome. Check if version is below 88.0.4324.96.Check Version:
chrome://version/Verify Fix Applied:
Confirm Chrome version is 88.0.4324.96 or higher in Settings > About Chrome.📡 Detection & Monitoring
Log Indicators:
- Chrome crash logs with speech recognizer components
- Unexpected Chrome process spawning with elevated privileges
Network Indicators:
- HTTP requests to known exploit domains
- Unusual outbound connections from Chrome processes
SIEM Query:
source="chrome_crash_logs" AND component="speech_recognizer" OR process_name="chrome" AND parent_process!="chrome"🔗 References
- https://chromereleases.googleblog.com/2021/01/stable-channel-update-for-desktop_19.html
- https://crbug.com/1131346
- https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-21124
- https://chromereleases.googleblog.com/2021/01/stable-channel-update-for-desktop_19.html
- https://crbug.com/1131346
- https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-21124
