Security readout for executives and security teams
Plain-English summary
A vulnerable Windows DNS server could be compromised remotely without a login or user action, potentially allowing server takeover and disruption or alteration of DNS-dependent operations. The 9.8 CVSS score makes this an urgent infrastructure risk, particularly where DNS is reachable from untrusted networks.
Executive priority
Treat as urgent. Direct infrastructure teams to identify affected DNS servers, confirm Microsoft update status, and remediate reachable or business-critical systems first. Require documented exceptions and compensating controls for systems that cannot be promptly patched.
Technical view
This is a remote code execution vulnerability in Windows DNS Server. Its CVSS 3.1 vector indicates network access, low attack complexity, no required privileges or user interaction, unchanged scope, and potentially high confidentiality, integrity, and availability impact. The supplied evidence does not describe the root cause.
Likely exposure
Likely exposure includes listed Windows Server 2008 SP2 through Windows Server 2019 releases, plus listed 1909, 2004, and 20H2 variants operating as DNS servers. Prioritize systems reachable from untrusted networks or supporting identity, directory, and business-critical services. Confirm exact applicability through Microsoft guidance.
Exploitation context
The supplied record is not marked as included in KEV, and no cited source states active exploitation. This does not prove exploitation has never occurred. Public proof-of-concept availability, exploit maturity, and observed attack activity are not established by the provided evidence.
Researcher notes
No CWE, root cause, vulnerable function, attack protocol detail, or technical trigger is supplied. The CVSS vector supports remote, unauthenticated, low-complexity assessment, but researchers should not infer exploit mechanics. Exact fixed builds and superseding updates must be confirmed through Microsoft’s advisory.
Mitigation direction
- Apply the Microsoft security update specified for the affected Windows Server version and installation type.
- If patching is delayed, consult Microsoft's advisory for supported mitigations and compensating controls.
- Restrict DNS service reachability to required clients while remediation is pending; do not treat this as a patch replacement.
- Prioritize unsupported, externally reachable, and business-critical DNS servers for immediate risk review.
Validation and detection
- Inventory Windows Server hosts running DNS Server and compare their releases with the supplied affected list.
- Verify installed security updates against Microsoft's advisory for each operating system and installation type.
- Review DNS network reachability, firewall policy, and exposure to untrusted clients.
- After remediation, revalidate update status and confirm DNS service health and expected resolution behavior.
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-2021-26895 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
- 9.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/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.
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:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C3.95.9microsoftVulnerability scoring details
Base CVSS 3.1 score
9.8CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/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
- Windows DNS Server Remote Code Execution VulnerabilityCVE reference, microsoft · vendor-advisory, patch
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26895CVE 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.