Known exploited vulnerability
CVE-2021-33766
The short answer
CVE-2021-33766 affects Microsoft Microsoft Exchange Server 2013 Cumulative Update 23 and is rated high (CVSS 7.3). CISA added it to the Known Exploited Vulnerabilities catalog on 2022-01-18: attackers are using it, so patch it first. The vendor has linked a patch.
What it is
Microsoft Exchange Server Information Disclosure Vulnerability
Severity
7.3 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Exploited (CISA KEV)
Yes, since Jan 18, 2022
Federal due date Feb 1, 2022
EPSS, next 30 days
98%
Higher than 100% of scored CVEs
How it can be exploited
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- Low
- Integrity impact
- Low
- Availability impact
- Low
What CISA says to do
Apply updates per vendor instructions.
Affected products
Microsoft Exchange Server 2013 Cumulative Update 23, Microsoft Exchange Server 2016 Cumulative Update 19, Microsoft Exchange Server 2016 Cumulative Update 20, Microsoft Exchange Server 2019 Cumulative Update 8, Microsoft Exchange Server 2019 Cumulative Update 9. NVD's record lists the exact affected versions.
References
- msrc.microsoft.com/update-guide/vulnerability/CVE-2021-33766 PatchVendor Advisory
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33766 PatchVendor Advisory
- www.zerodayinitiative.com/advisories/ZDI-21-798/ Third Party AdvisoryVDB Entry
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33766 US Government Resource
Questions
Is CVE-2021-33766 being exploited?
Yes. CISA added CVE-2021-33766 to its Known Exploited Vulnerabilities catalog on 2022-01-18, with a federal remediation due date of 2022-02-01.
How do I fix CVE-2021-33766?
CISA's required action: Apply updates per vendor instructions.
From NVD, CISA KEV, FIRST EPSS and OSV.dev, checked . Status on NVD: Analyzed. The description is NVD's text, quoted as published.
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