Known exploited vulnerability
CVE-2021-31207
The short answer
CVE-2021-31207 affects Microsoft Microsoft Exchange Server 2013 Cumulative Update 23 and is rated medium (CVSS 6.6). 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 Security Feature Bypass Vulnerability
Weakness: CWE-434.
Severity
6.6 medium
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
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
- Network
- Attack complexity
- High
- Privileges required
- High
- User interaction
- None
- 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 23, Microsoft Exchange Server 2019 Cumulative Update 9, Microsoft Exchange Server 2016 Cumulative Update 20, Microsoft Exchange Server 2016 Cumulative Update 19, Microsoft Exchange Server 2019 Cumulative Update 8. NVD's record lists the exact affected versions.
References
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207 PatchVendor Advisory
- www.zerodayinitiative.com/advisories/ZDI-21-819/ Third Party AdvisoryVDB Entry
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207 PatchVendor Advisory
- www.zerodayinitiative.com/advisories/ZDI-21-819/ Third Party AdvisoryVDB Entry
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31207 US Government Resource
Questions
Is CVE-2021-31207 being exploited?
Yes. CISA added CVE-2021-31207 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-2021-31207?
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.