CVE-2021-31196: Microsoft Exchange Server remote code execution flaw

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 17 September 2026. Confidence: medium.

high priorityIt is a network-reachable remote code execution flaw in Exchange with confirmed exploitation per CISA KEV and very high EPSS, though it requires high privileges.

What it is

CVE-2021-31196 is a remote code execution vulnerability in Microsoft Exchange Server. The record gives only a one-line description and no root-cause detail, so the exact vulnerable component is not specified. It matters because it is listed in CISA's Known Exploited Vulnerabilities catalog, meaning it has been exploited in the wild.

Impact

Successful exploitation allows an attacker to execute code on the Exchange server, giving control over mail data and the host. The CVSS vector rates confidentiality, integrity and availability impact as high.

Attack surface

The vector is network-reachable (AV:N) with no user interaction (UI:N), but requires high privileges (PR:H), so an attacker needs an already privileged account or role on the target. No authentication bypass is implied by the record.

Exploitation

CISA added it to the KEV catalog on 2024-08-21 with a 2024-09-11 remediation due date, and EPSS gives a 30-day probability of about 0.54 (98.9th percentile). No ransomware campaign use is recorded.

What to do

• Apply the Microsoft Exchange Server security update referenced in the MSRC advisory for CVE-2021-31196.
• If patching is not immediately possible, apply the vendor mitigations or discontinue use of the affected product per CISA's required action.
• Restrict and audit privileged Exchange roles and administrative access to reduce the high-privilege precondition.
• Monitor Microsoft and CISA guidance for updated remediation steps given the KEV listing.

Detection

• Hunt for unexpected process creation or child processes spawned by Exchange server processes (for example w3wp.exe) on mailbox and Edge Transport servers.
• Review Exchange and Windows event logs for anomalous privileged account activity around the patch window and after.
• Alert on exploitation attempts or scanning against Exchange endpoints using available network and IIS logs.
• Track patch status of Exchange servers against the MSRC update to confirm remediation.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.