Known exploited vulnerability
CVE-2021-26858
The short answer
CVE-2021-26858 affects Microsoft Microsoft Exchange Server 2013 Cumulative Update 21 and is rated high (CVSS 7.8). 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 Remote Code Execution Vulnerability
Severity
7.8 high
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Exploited (CISA KEV)
Yes, since Nov 3, 2021
Federal due date May 3, 2022
EPSS, next 30 days
94%
Higher than 100% of scored CVEs
How it can be exploited
- Attack vector
- Local
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
What CISA says to do
Apply updates per vendor instructions.
Affected products
Microsoft Exchange Server 2013 Cumulative Update 21, Microsoft Exchange Server 2013 Cumulative Update 22, Microsoft Exchange Server 2013 Cumulative Update 23, Microsoft Exchange Server 2016 Cumulative Update 10, Microsoft Exchange Server 2016 Cumulative Update 11, Microsoft Exchange Server 2016 Cumulative Update 12, Microsoft Exchange Server 2016 Cumulative Update 13, Microsoft Exchange Server 2016 Cumulative Update 14, Microsoft Exchange Server 2016 Cumulative Update 15, Microsoft Exchange Server 2016 Cumulative Update 16, Microsoft Exchange Server 2016 Cumulative Update 17, Microsoft Exchange Server 2016 Cumulative Update 18. NVD's record lists the exact affected versions.
References
- msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858 PatchVendor Advisory
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858 PatchVendor Advisory
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858 US Government Resource
Questions
Is CVE-2021-26858 being exploited?
Yes. CISA added CVE-2021-26858 to its Known Exploited Vulnerabilities catalog on 2021-11-03, with a federal remediation due date of 2022-05-03. CISA lists it as used in ransomware campaigns.
How do I fix CVE-2021-26858?
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.
Related
Latest CVEs this week
Critical and High CVEs from the last 7 days, with KEV and EPSS.
Exploited vulnerabilities by vendor
Every vendor in CISA's KEV catalog, with its count.
Microsoft exploited vulnerabilities
Everything CISA lists as exploited for Microsoft.
Vulnerability watch
A briefing and a fix pull request when an advisory hits your dependencies.
Know the day a CVE lands in your code
Connect a GitHub repository and ZeusQA checks its dependencies daily, briefs each advisory and opens the fix. Three test runs free, no card.