Known exploited vulnerability
CVE-2021-34523
The short answer
CVE-2021-34523 affects Microsoft Microsoft Exchange Server 2013 Cumulative Update 23 and is rated critical (CVSS 9.0). CISA added it to the Known Exploited Vulnerabilities catalog on 2021-11-03: attackers are using it, so patch it first. The vendor has linked a patch.
What it is
Microsoft Exchange Server Elevation of Privilege Vulnerability
Severity
9.0 critical
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Exploited (CISA KEV)
Yes, since Nov 3, 2021
Federal due date Nov 17, 2021
EPSS, next 30 days
100%
Higher than 100% of scored CVEs
How it can be exploited
- Attack vector
- Local
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- None
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-2021-34523 PatchVendor Advisory
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34523 PatchVendor Advisory
- www.zerodayinitiative.com/advisories/ZDI-21-822/ Third Party AdvisoryVDB Entry
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34523 US Government Resource
Questions
Is CVE-2021-34523 being exploited?
Yes. CISA added CVE-2021-34523 to its Known Exploited Vulnerabilities catalog on 2021-11-03, with a federal remediation due date of 2021-11-17. CISA lists it as used in ransomware campaigns.
How do I fix CVE-2021-34523?
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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