#VU52377 Path traversal in SonicWall On-premise Email Security (ES) and SonicWall Hosted Email Security (HES) - CVE-2021-20023

Vulnerability identifier: #VU52377

Vulnerability risk: High

CVSSv4.0: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:A/U:Amber]

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: SonicWall

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

SonicWall On-premise Email Security (ES): before 10.0.9.6173

SonicWall Hosted Email Security (HES): before 10.0.9.6173

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External links
https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0010
https://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.