Vulnerability identifier: #VU52377

Vulnerability risk: High

CVSSv3.1: 6.5 [CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:N/A:N/E:H/RL:O/RC:C]

CVE-ID: CVE-2021-20023

CWE-ID: CWE-22

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
SonicWall On-premise Email Security (ES)
Client/Desktop applications / Antivirus software/Personal firewalls
SonicWall Hosted Email Security (HES)
Client/Desktop applications / Antivirus software/Personal firewalls

Vendor:

Description

The vulnerability allows a remote user to perform directory traversal attacks.

The vulnerability exists due to input validation error when processing directory traversal sequences within the "branding"  feature. A remote authenticated user can send a specially crafted HTTP request and read arbitrary files on the system with NT AUTHORITY\SYSTEM account.

Request example:

https://<SonicWall ES host>/dload_apps?action=<any value>&path=..%2F..%2F..%2F..%2F..%2Fwindows%2Fsystem32%2Fcalc.exe&id=update

Note, the vulnerability is being actively exploited in the wild.

Mitigation
Install update from vendor's website.

Vulnerable software versions

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External links
http://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0010
http://www.fireeye.com/blog/threat-research/2021/04/zero-day-exploits-in-sonicwall-email-security-lead-to-compromise.html

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote authenticated privileged user via the Internet.

Is there known malware, which exploits this vulnerability?

Yes. This vulnerability is being exploited in the wild.