CVE-2021-26857 Microsoft Exchange Server Remote Code Execution
Attackers can execute arbitrary code on Microsoft Exchange Server via unsafe deserialization, requiring immediate patching.
- Exploited in the wild
- Since 3 Nov 2021
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2021-26857?
CVE-2021-26857 is a high-severity unsafe deserialization vulnerability in Microsoft Exchange Server, published on 2 Mar 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
Microsoft Exchange Server Remote Code Execution Vulnerability
Weakness: CWE-502
Which versions are affected by CVE-2021-26857?
It affects 1 product.
Products include Microsoft Exchange Server.
How do I fix CVE-2021-26857?
No fix has been published for CVE-2021-26857 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 3 May 2022.
Upgrade, and only deserialise data from trusted sources or with an allow-list of types. More about Unsafe deserialization.
Is CVE-2021-26857 being exploited?
Yes. Attackers have exploited CVE-2021-26857 in the wild since at least 3 Nov 2021, including in ransomware campaigns.
Public exploit code: 1 proofs of concept on GitHub.
Other vulnerabilities in Microsoft Exchange Server
- CVE-2024-21410 Microsoft Exchange Server Privilege Escalation
- CVE-2021-34473 Microsoft Exchange Server Remote Code Execution
- CVE-2021-26855 Microsoft Exchange Server Remote Code Execution
- CVE-2021-34523 Microsoft Exchange Server Privilege Escalation
- CVE-2023-21529 Microsoft Exchange Server Deserialization of Untrusted Data
Sources
Also known as GHSA-2qwq-gqpm-q83g.