Security readout for executives and security teams
Plain-English summary
A critical Microsoft Exchange Server flaw could allow a highly privileged attacker to execute code remotely, potentially compromising email, sensitive data, and server availability. The supplied CVSS score is 9.1. Prioritize listed on-premises Exchange versions, but do not assume exposure without verifying deployed cumulative updates and patch status.
Executive priority
Treat as an urgent remediation item where affected Exchange builds are present, especially on externally reachable or business-critical mail servers. The impact can span data theft, unauthorized modification, and service disruption. Confirm exposure immediately and use Microsoft's advisory to drive patching; active exploitation is not established by this bundle.
Technical view
CVE-2021-26412 is a network-reachable remote code execution vulnerability. Its CVSS vector indicates low attack complexity, high privileges required, no user interaction, changed scope, and high confidentiality, integrity, and availability impact. The bundle identifies specific Exchange Server 2013, 2016, and 2019 cumulative updates as affected.
Likely exposure
Potential exposure is limited to organizations running the listed Exchange cumulative updates: 2013 CU23; 2016 CU18 or CU19; and 2019 CU7 or CU8. Internet accessibility may increase practical risk, but the supplied evidence does not establish which Exchange interfaces or configurations are required.
Exploitation context
The supplied record says this CVE is not in KEV. Its CVSS vector records proof-of-concept exploit maturity, but the bundle provides no evidence of active exploitation. High attacker privileges are required, which may constrain initial access while making compromised administrative credentials or an existing foothold relevant.
Researcher notes
The source bundle provides no CWE, attack-path detail, affected component, or configuration prerequisites. Analysis should therefore remain at the CVSS and product-version level. The unusual version strings are bundle-provided; validate exact build and update applicability against Microsoft's advisory before making exposure decisions.
Mitigation direction
- Identify Exchange servers running the affected cumulative updates.
- Apply the Microsoft security update referenced by the vendor advisory.
- Follow current Microsoft guidance for unsupported or superseded Exchange builds.
- Restrict unnecessary network access to Exchange while remediation is pending.
Validation and detection
- Inventory Exchange editions, cumulative updates, and installed security updates.
- Compare every server's status with the Microsoft advisory.
- Confirm the applicable Microsoft security update installed successfully.
- Review relevant Exchange and system logs for unexpected privileged activity.
- Reassess externally reachable Exchange services after remediation.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
Execution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-26412 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H/E:P/RL:O/RC:C
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H/E:P/RL:O/RC:C2.36microsoftVulnerability scoring details
Base CVSS 3.1 score
9.1CriticalVector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H/E:P/RL:O/RC:C
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- Microsoft Exchange Server Remote Code Execution VulnerabilityCVE reference, microsoft · vendor-advisory, patch
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26412CVE reference, CVE · x_refsource_MISC, x_transferred
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.