CVE-2020-9920 – This vulnerability allows a malicious mail serv... (How to Fix)

Q: What is the severity of CVE-2020-9920?

CVE-2020-9920 has a CVSS score of 9.1 (CRITICAL). This vulnerability allows a malicious mail server to overwrite arbitrary files on Apple devices through a path handling issue in mail processing. It affects iOS, iPadOS, macOS Catalina, and watchOS users who use the built-in Mail app. The attacker could potentially replace legitimate mail files with malicious content.

📋 TL;DR

This vulnerability allows a malicious mail server to overwrite arbitrary files on Apple devices through a path handling issue in mail processing. It affects iOS, iPadOS, macOS Catalina, and watchOS users who use the built-in Mail app. The attacker could potentially replace legitimate mail files with malicious content.

💻 Affected Systems

Products:

iOS
iPadOS
macOS Catalina
watchOS

Versions: Versions prior to iOS 13.6, iPadOS 13.6, macOS Catalina 10.15.6, watchOS 6.2.8

Operating Systems: iOS, iPadOS, macOS, watchOS

Default Config Vulnerable: ⚠️ Yes

Notes: Affects default Mail app configurations when connecting to mail servers

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete system compromise through arbitrary file overwrite leading to remote code execution or data destruction

🟠

Likely Case

Mail data corruption, potential credential theft if malicious files replace legitimate mail content

🟢

If Mitigated

Limited to mail app sandbox if proper app sandboxing is enforced

🌐 Internet-Facing: HIGH - Exploitable via malicious mail server which is internet-facing

🏢 Internal Only: LOW - Requires interaction with external mail server

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires control of mail server or man-in-the-middle position between client and legitimate mail server

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: iOS 13.6, iPadOS 13.6, macOS Catalina 10.15.6, watchOS 6.2.8

Vendor Advisory: https://support.apple.com/kb/HT211288

Restart Required: Yes

Instructions:

1. Go to Settings > General > Software Update on iOS/iPadOS/watchOS. 2. Install available updates. 3. For macOS, go to System Preferences > Software Update. 4. Install macOS Catalina 10.15.6 or later.

🔧 Temporary Workarounds

Use alternative mail client

all

Temporarily switch to third-party mail applications not affected by this vulnerability

Disable automatic mail fetching

all

Manually check mail instead of automatic background fetching

🧯 If You Can't Patch

Restrict mail app network access using firewall rules
Use VPN for all mail server connections to prevent MITM attacks

🔍 How to Verify

Check if Vulnerable:

Check device version in Settings > General > About on iOS/iPadOS/watchOS or About This Mac on macOS

Check Version:

sw_vers (macOS) or Settings > General > About > Version (iOS/iPadOS/watchOS)

Verify Fix Applied:

Confirm version is iOS 13.6+, iPadOS 13.6+, macOS Catalina 10.15.6+, or watchOS 6.2.8+

📡 Detection & Monitoring

Log Indicators:

Unusual mail app crashes
Unexpected file write operations in mail app sandbox

Network Indicators:

Connections to suspicious mail servers
Unusual mail protocol traffic patterns

SIEM Query:

source="apple_mail" AND (event="crash" OR event="file_write") AND path NOT LIKE "%/Mail/%"

📊 Metadata

CVE ID: CVE-2020-9920

CVSS v3 Score: 9.1 (CRITICAL)

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

CWE: CWE-22

Published: October 22, 2020

Last Updated: November 21, 2024

🔗 References

https://support.apple.com/kb/HT211288 Vendor Advisory
https://support.apple.com/kb/HT211289 Vendor Advisory
https://support.apple.com/kb/HT211291 Vendor Advisory
https://support.apple.com/kb/HT211288 Vendor Advisory
https://support.apple.com/kb/HT211289 Vendor Advisory
https://support.apple.com/kb/HT211291 Vendor Advisory

📤 Share & Export

📄 Export Markdown 📋 Export JSON

🔗 Related Vulnerabilities

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