CVE-2021-33766
Published: January 18, 2022
Official Description
Microsoft Exchange Server contains an information disclosure vulnerability which can allow an unauthenticated attacker to steal email traffic from target.
CISA KEV Advisory
Microsoft Exchange Server Information Disclosure
Microsoft Exchange Server contains an information disclosure vulnerability which can allow an unauthenticated attacker to steal email traffic from target.
Apply updates per vendor instructions.
Risk Analysis
Microsoft Exchange Server contains an information disclosure vulnerability that allows an unauthenticated attacker to steal email traffic. With an EPSS score of 0.93483 and its presence in CISA's KEV, this vulnerability is highly likely to be exploited and poses a critical risk to data confidentiality. The ability for an unauthenticated attacker to access email traffic is a severe security concern.
This vulnerability is actively exploited in the wild. The fact that an unauthenticated attacker can exploit this remotely indicates a broad attack surface.
Administrators must apply the latest security updates for Microsoft Exchange Server to address this information disclosure vulnerability. Implementing network segmentation and monitoring for unusual traffic patterns can also help detect and prevent exploitation.
Technical Analysis
CVE-2021-33766 requires local access, meaning attackers must already have a foothold on the target system.
Exploitation requires some privileges, which limits the exposure to scenarios where an attacker has already gained initial access.
CISA has added CVE-2021-33766 to the Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. U.S. federal agencies are required to patch this within the mandated timeframe, and all organizations should treat remediation as urgent.
Affected Vendors & Products
Exploit & PoC Resources
All References (1)
Quick Facts
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2021-33766 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts
- !CISA KEV: Federal agencies must patch per BOD 22-01 timeline
- !Active exploitation confirmed — treat as P1