CVE-2020-1520: Microsoft Windows 10 RCE Vulnerability

CVE-2020-1520 Overview

A remote code execution vulnerability exists when the Windows Font Driver Host improperly handles memory. An attacker who successfully exploited this vulnerability would gain execution on a victim system, potentially allowing them to install programs, view, change, or delete data, or create new accounts with full user rights. The security update addresses the vulnerability by correcting how the Windows Font Driver Host handles memory.

Critical Impact

Successful exploitation allows attackers to execute arbitrary code on victim systems through improper memory handling in the Windows Font Driver Host component.

Affected Products

• Microsoft Windows 10 (all versions including 1607, 1709, 1803, 1809, 1903, 1909, 2004)
• Microsoft Windows 7 SP1
• Microsoft Windows 8.1
• Microsoft Windows RT 8.1
• Microsoft Windows Server 2008 SP2 and R2 SP1
• Microsoft Windows Server 2012 and R2
• Microsoft Windows Server 2016 (including 1903, 1909, 2004)
• Microsoft Windows Server 2019

Discovery Timeline

• August 17, 2020 - CVE-2020-1520 published to NVD
• February 23, 2026 - Last updated in NVD database

Technical Details for CVE-2020-1520

Vulnerability Analysis

This vulnerability resides in the Windows Font Driver Host (fontdrvhost.exe), a critical system component responsible for processing font-related operations. The Font Driver Host runs in user mode and handles font rendering requests, serving as an isolation boundary between font processing and the kernel.

The flaw stems from improper memory handling within the font processing routines. When the Font Driver Host processes specially crafted font data, it fails to properly validate or manage memory operations, leading to memory corruption. This corruption can be leveraged by an attacker to achieve arbitrary code execution within the context of the Font Driver Host process.

The local attack vector means an attacker must either have local access to the system or convince a user to open a malicious document containing specially crafted fonts. The vulnerability requires low privileges to exploit and does not require user interaction once the malicious content reaches the target system.

Root Cause

The root cause of CVE-2020-1520 is improper memory handling in the Windows Font Driver Host component. Specifically, the font processing routines fail to properly manage memory during font parsing operations. This can result in memory corruption conditions when processing malformed or malicious font data. The absence of proper bounds checking or memory validation allows attackers to manipulate memory in ways that lead to code execution.

Attack Vector

The attack vector for this vulnerability is local, requiring an attacker to have some level of access to the target system or to deliver malicious content that gets processed locally. Typical exploitation scenarios include:

1. Delivering a malicious document (e.g., Word, PDF) containing embedded crafted fonts
2. Hosting a webpage with malicious web fonts that get processed by the victim's browser
3. Placing malicious font files in locations where they will be automatically loaded

Once the malicious font data is processed by the Windows Font Driver Host, the memory handling flaw can be triggered, allowing the attacker to execute arbitrary code with the privileges of the current user.

The vulnerability mechanism involves the Font Driver Host's memory management routines. When processing crafted font data, improper validation allows memory corruption that can be exploited for code execution. For detailed technical information, see the Microsoft Security Advisory.

Detection Methods for CVE-2020-1520

Indicators of Compromise

• Unusual crashes or unexpected behavior of fontdrvhost.exe process
• Suspicious font files appearing in system directories or user temp folders
• Memory access violations logged in Windows Event Viewer related to font processing
• Unexpected child processes spawned from fontdrvhost.exe

Detection Strategies

• Monitor for abnormal process behavior from fontdrvhost.exe, including unusual memory consumption or child process creation
• Deploy endpoint detection rules to identify exploitation attempts targeting font processing components
• Implement file integrity monitoring for system font directories (C:\Windows\Fonts)
• Enable Windows Defender Exploit Guard to detect memory corruption attempts

Monitoring Recommendations

• Configure Windows Event Log monitoring for Application crashes related to font driver components
• Enable advanced audit policies to track file system access to font directories
• Deploy memory protection monitoring solutions to detect heap corruption attempts
• Utilize SentinelOne's behavioral AI to identify anomalous activities from font processing components

How to Mitigate CVE-2020-1520

Immediate Actions Required

• Apply the security update from Microsoft immediately to all affected Windows systems
• Prioritize patching for systems that process untrusted documents or browse untrusted websites
• Implement network segmentation to limit lateral movement if systems cannot be immediately patched
• Enable Windows Defender Exploit Guard mitigations including CFG and ASLR enforcement

Patch Information

Microsoft has released security updates to address this vulnerability as part of their August 2020 security updates. The patch corrects how the Windows Font Driver Host handles memory operations. Administrators should apply the appropriate update for their Windows version through Windows Update, WSUS, or by downloading directly from the Microsoft Security Advisory for CVE-2020-1520.

Workarounds

• Restrict access to untrusted font files by implementing application whitelisting
• Disable the Windows Font Cache Service temporarily if patching is delayed (may impact performance)
• Block potentially malicious documents at email and web gateways before they reach endpoints
• Consider implementing Protected View in Microsoft Office to prevent automatic font loading from untrusted documents

# Verify Windows Font Driver Host service status and disable if needed
sc query FontCache
sc config FontCache start= disabled
sc stop FontCache

# Note: Disabling Font Cache may impact system performance and font rendering
# Apply Microsoft security update as soon as possible instead