CVE-2021-24026 – This vulnerability allows remote code execution... (How to Fix)

Q: What is the severity of CVE-2021-24026?

CVE-2021-24026 has a CVSS score of 9.8 (CRITICAL). This vulnerability allows remote code execution via WhatsApp voice calls due to a missing bounds check in the audio decoding pipeline. An attacker could send a malicious audio packet during a call to trigger an out-of-bounds write and potentially execute arbitrary code on the victim's device. All WhatsApp users on affected Android and iOS versions are vulnerable.

📋 TL;DR

This vulnerability allows remote code execution via WhatsApp voice calls due to a missing bounds check in the audio decoding pipeline. An attacker could send a malicious audio packet during a call to trigger an out-of-bounds write and potentially execute arbitrary code on the victim's device. All WhatsApp users on affected Android and iOS versions are vulnerable.

💻 Affected Systems

Products:

WhatsApp for Android
WhatsApp Business for Android
WhatsApp for iOS
WhatsApp Business for iOS

Versions: Android prior to v2.21.3, iOS prior to v2.21.32

Operating Systems: Android, iOS

Default Config Vulnerable: ⚠️ Yes

Notes: All default configurations are vulnerable; no special settings required for exploitation.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote attacker gains full control of victim's device through WhatsApp call, leading to data theft, surveillance, or further network compromise.

🟠

Likely Case

Remote code execution allowing installation of malware, data exfiltration, or device takeover.

🟢

If Mitigated

Attack prevented by updated WhatsApp version; no impact with proper patching.

🌐 Internet-Facing: HIGH - Exploitable via internet calls to any WhatsApp user.

🏢 Internal Only: LOW - No internal-only exploitation vector; requires external attacker.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires initiating or receiving a WhatsApp call; no authentication needed beyond standard call functionality.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Android v2.21.3+, iOS v2.21.32+

Vendor Advisory: https://www.whatsapp.com/security/advisories/2021/

Restart Required: No

Instructions:

1. Open Google Play Store or Apple App Store. 2. Search for WhatsApp. 3. Tap Update. 4. Ensure version is Android v2.21.3+ or iOS v2.21.32+.

🔧 Temporary Workarounds

Disable WhatsApp Calls

all

Prevent exploitation by disabling voice call functionality.

🧯 If You Can't Patch

Block WhatsApp voice calls at network perimeter using DPI or application control.
Use mobile device management to restrict WhatsApp installation on corporate devices.

🔍 How to Verify

Check if Vulnerable:

Check WhatsApp version in app settings: Settings > Help > App Info.

Check Version:

Not applicable - check via app interface.

Verify Fix Applied:

Confirm WhatsApp version is Android v2.21.3+ or iOS v2.21.32+.

📡 Detection & Monitoring

Log Indicators:

Unusual process creation from WhatsApp, abnormal memory access patterns in system logs.

Network Indicators:

Suspicious audio packet patterns in WhatsApp call traffic, unexpected outbound connections post-call.

SIEM Query:

Not applicable - mobile endpoint detection required.

📊 Metadata

CVE ID: CVE-2021-24026

CVSS v3 Score: 9.8 (CRITICAL)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-787

Published: April 6, 2021

Last Updated: November 21, 2024

🔗 References

https://www.whatsapp.com/security/advisories/2021/ Vendor Advisory
https://www.whatsapp.com/security/advisories/2021/ Vendor Advisory

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