Used in attacks· fix by 2021-12-01Not scored yetUsed by ransomware gangs
Microsoft Exchange
CVE-2021-42321
An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.
What this means for your business
- It affects Microsoft Exchange. It matters if your company, or a supplier that handles your data, runs it.
- Attackers are already using it. CISA added it to its list of flaws used in real attacks on 17 November 2021.
- Ransomware gangs are known to have used it.
- FIRST's prediction model gives it a 92% chance of attack attempts being seen in the next 30 days, ranking above 99% of all known flaws.
What to do
- 1Check whether your company or your suppliers run Microsoft Exchange.
- 2If you do, follow CISA's required action below. No patch reference has been published yet.
- 3Treat it as urgent. US federal agencies must fix it by 1 December 2021. That deadline does not apply to private companies, but it shows how seriously CISA takes it.
- 4Because attackers have used it, check the affected systems for signs of a break-in, not only for the update.
Not sure if your company is exposed?
Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.
Required action
Apply updates per vendor instructions.
CISA’s wording, unedited.
Scoring
- CVSS
- Not yet scored
Dates
- Published
- 2021-11-17
- Added to KEV
- 2021-11-17
- Remediation due
- 2021-12-01
- Sources
- CISA KEV