CVE-2021-33766 on CISA KEV

Microsoft Exchange Server Information Disclosure Vulnerability

01What CISA says about this vulnerability

Microsoft Exchange Server Information Disclosure Vulnerability

02Required action — verbatim from CISA

Apply updates per vendor instructions.

03Notes & references

• portal.msrc.microsoft.com — https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-3376…
• www.zerodayinitiative.com — https://www.zerodayinitiative.com/advisories/ZDI-21-798/

04SARA's analyst layer — why this matters

This vulnerability is currently on the CISA KEV list, which CISA only adds CVEs to when there is reliable evidence of active exploitation in the wild. For federal civilian agencies, BOD 22-01 requires remediation by the due date above. For everyone else, KEV is the strongest "patch immediately" signal you can get from public threat intel.

05Affected products (summary)

Vendor	Product	Versions
Microsoft	Microsoft Exchange Server 2019 Cumulative Update 9	15.02.0
Microsoft	Microsoft Exchange Server 2016 Cumulative Update 20	15.01.0
Microsoft	Microsoft Exchange Server 2013 Cumulative Update 23	15.00.0
Microsoft	Microsoft Exchange Server 2016 Cumulative Update 19	15.01.0
Microsoft	Microsoft Exchange Server 2019 Cumulative Update 8	15.02.0

06Detection

Open the Sigma generator with a pre-filled prompt for this CVE to draft a starting detection:

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