CVE-2021-42321Microsoft Exchange Server Remote Code Execution Vulnerability
CVE-2021-42321 is a vulnerability in Microsoft Exchange, rated high (8.8 on CVSS 3.1).
Why this priority: Exploited in the wild: listed in CISA's KEV catalog.
Published · Updated · NVD status: Analyzed
What it is
The record does not classify the weakness yet; the description below says what the reporter found.
How it is reached
An attacker can exploit it over the network, with an ordinary user account, and nobody has to click anything.
What an attacker gains
A successful attack can read the data it protects, change data or behaviour and take it offline.
Is it being exploited?
CISA added it to the Known Exploited Vulnerabilities catalog on 2021-11-17: it is being exploited in the wild. CISA links it to ransomware campaigns. EPSS estimates a 92% chance of exploitation activity in the next 30 days, higher than 100% of scored CVEs.
What to do
- Treat it as urgent: it is on CISA's KEV list. CISA's deadline for US federal agencies: 2021-12-01.
- Apply the update for your edition of Microsoft Exchange. Fixed builds: Microsoft Exchange Server 2016 Cumulative Update 21: 15.01.2308.020; Microsoft Exchange Server 2016 Cumulative Update 22: 15.01.2375.017; Microsoft Exchange Server 2019 Cumulative Update 10: 15.02.0792.019; Microsoft Exchange Server 2019 Cumulative Update 11: 15.02.0986.014. The patch notes are linked below.
- Until it is patched, review who holds accounts that can reach it.
- Check exposed instances for signs of compromise, not only for the version.
Description from NVD
Microsoft Exchange Server Remote Code Execution Vulnerability
What this means for your architecture.
A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.
Components it touches
- Microsoft Exchange. Start from where it runs and what it is connected to.
Trust boundaries in play
- Authenticated network access. An account is needed, so exposure follows who can sign in: customers, partners or staff.
Questions to answer about your own systems
- Where does Microsoft Exchange run in your systems, and at which version?
- Which of those instances can be reached from the internet or partner networks?
- What can it reach once compromised: which data stores, secrets and services?
Read more
Patches and commits
Sources
- CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
- Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
- Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
- Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.