#VU53082 Improper validation of integrity check value in Microsoft Exchange Server - CVE-2021-31209

Vulnerability identifier: #VU53082

Vulnerability risk: Medium

CVSSv4.0: 6.3 [CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2021-31209

CWE-ID: CWE-354

Exploitation vector: Local network

Exploit availability: No

Vulnerable software:
Microsoft Exchange Server
Server applications / Mail servers

Vendor: Microsoft

Description

The vulnerability allows a remote attacker to bypass integrity checks.

The vulnerability exists within the handling of Exchange Server Help updates. A remote attacker on the local network can bypass integrity check on update downloads.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Microsoft Exchange Server: 2013 Cumulative Update 23 15.00.1497.002, 2016 Cumulative Update 19 15.01.2176.002 - 2016 Cumulative Update 20 15.01.2242.004, 2019 Cumulative Update 8 15.02.0792.003 - 2019 Cumulative Update 9 15.02.0858.005

---

External links
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31209
https://www.zerodayinitiative.com/advisories/ZDI-21-615/

---

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the local network (LAN).

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.