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CVE-2021-33766: Microsoft Exchange Server Information Disclosure

criticalknown exploitedpublic exploitCVE-2021-33766
Actively exploited. At least one CVE in this advisory is listed in the CISA Known Exploited Vulnerabilities catalog — exploitation has been observed in the wild. Treat remediation as urgent.
Microsoft Exchange Server contains an information disclosure vulnerability which can allow an unauthenticated attacker to steal email traffic from target.

CSIRTS triage

vendor: Microsoftproduct: Exchange ServerInformation disclosure
What
Microsoft Exchange Server contains an information disclosure vulnerability that can allow an unauthenticated attacker to steal email traffic.
Who is affected
Deployments of Microsoft Exchange Server.
Urgency
Remediation is urgent due to active exploitation and critical severity.
Action
Apply the latest security updates from Microsoft.

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Details

Source
CISA Known Exploited Vulnerabilities (US · database · site)
Severity
critical
Published
2022-01-18
Exploitation
Observed in the wild (CISA KEV)

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-33766

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Referenced CVEs

CVECSIRTS overviewExternal
CVE-2021-33766coverage & exploitation statusNVD · CVE.org

Recent advisories for Microsoft Exchange Server

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

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