Buffer overflow vulnerability in SonicWall products (CVE-2021-20027)

A buffer overflow vulnerability in SonicOS could allow a remote attacker to cause a Denial of Service (DoS) by sending a specially crafted request to the firewall’s web interface. This vulnerability affects SonicOS Gen5, Gen6, Gen7 platforms, and SonicOSv virtual firewalls.

• SonicWall PSIRT is not aware of any active exploitation of this vulnerability in the wild
• No reports of a PoC have been made public at the time of this advisory

Affected Software / System

This advisory specifically applies to the following SonicWall products:

CVE

CVE-2021-20027

Type

Buffer overflow vulnerability

Exploit Status: 

Not known to be exploited in the wild yet

Rating

CVSS Score of 7.5/10 (High)

Impact

The vulnerability requires Web Management to be enabled on the WAN/LAN interface and for there to be an ongoing active management session. This scenario can exist 1) if an administrator is logged into the web interface or 2) if Global Management System (GMS) / Network Security Manager (NSM) are configured to manage the firewall over HTTPS on the WAN interface.

If WAN management is disabled on the firewall the GMS/NSM management modes listed below are not impacted:

• GMS IPSec tunnel mode
• GMS Existing VPN tunnel mode
• GMS Zero Touch
• NSM Zero Touch
• GMS Management (Zero Touch Mode)
• NSM Management (Zero Touch Mode)

The SSL-VPN portal on the firewall, Virtual Office, is NOT affected.

Mitigation

Ingalls strongly recommends that affected clients apply the SonicOS Firmware updates ASAP. If this is not possible, Ingalls recommends following SonicWall’s recommendation that administrators limit SonicOS management access to trusted sources (and/or disable management access from untrusted internet sources) by modifying the existing SonicOS Management access rules (SSH/HTTPS/HTTP Management). This will only allow management access from trusted source IP addresses.

Ingalls recommends the following actions:

Updating SonicOS Firmware (Recommended)

FIXED SOFTWARE: