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CVE-2021-31207 Microsoft CVE debrief

CVE-2021-31207 is a Microsoft Exchange Server security feature bypass vulnerability that CISA added to its Known Exploited Vulnerabilities catalog on 2021-11-03. The KEV entry indicates known exploitation and sets a remediation due date of 2021-11-17, with CISA’s required action to apply updates per vendor instructions. The supplied corpus also marks this vulnerability as associated with known ransomware campaign use, so defenders should treat it as a high-priority patching item.

Vendor
Microsoft
Product
Exchange Server
CVSS
Unknown
CISA KEV
Listed
Original CVE published
2021-11-03
Original CVE updated
2021-11-03
Advisory published
2021-11-03
Advisory updated
2021-11-03

Who should care

Administrators and security teams responsible for Microsoft Exchange Server, especially organizations with internet-facing deployments or systems tracked under CISA KEV.

Technical summary

The supplied sources identify a Microsoft Exchange Server security feature bypass vulnerability. CISA’s KEV record confirms it as a known exploited vulnerability and points to vendor-directed updating as the remediation path. The corpus does not provide lower-level exploit mechanics, so this summary is limited to exposure, prioritization, and defensive response.

Defensive priority

High. A KEV-listed Microsoft Exchange Server vulnerability with known exploitation and known ransomware campaign use should be prioritized for immediate patching and validation, especially relative to the 2021-11-17 due date.

Recommended defensive actions

  • Apply Microsoft’s Exchange Server updates and vendor guidance as soon as possible.
  • Inventory all Exchange Server instances, including legacy, hybrid, and partially managed deployments.
  • Prioritize internet-facing Exchange systems for verification and remediation.
  • Confirm remediation before and after patching, and track any overdue systems against the CISA KEV due date of 2021-11-17.
  • Review incident response and monitoring coverage for Exchange Server systems while remediation is underway.

Evidence notes

CISA’s Known Exploited Vulnerabilities feed lists CVE-2021-31207 as "Microsoft Exchange Server Security Feature Bypass Vulnerability," with dateAdded 2021-11-03, dueDate 2021-11-17, knownRansomwareCampaignUse set to "Known," and requiredAction "Apply updates per vendor instructions." The source notes point to the NVD detail page. The provided record does not include CVSS or deeper technical mechanics.

Official resources

Publicly disclosed and added to CISA KEV on 2021-11-03, with remediation due by 2021-11-17.