Security readout for executives and security teams
Plain-English summary
A remote attacker could potentially take control of an unpatched Windows server providing DNS, without credentials or user interaction. Successful exploitation could expose data, alter systems, or interrupt DNS and dependent business services. The supplied evidence does not establish active exploitation.
Executive priority
Treat as an urgent patching priority because compromise of DNS infrastructure can disrupt authentication, application access, and core network operations. Prioritize externally reachable and high-dependency DNS servers first. Escalate any unsupported affected release for replacement or vendor-supported remediation planning.
Technical view
CVE-2021-26877 is an unauthenticated, network-accessible remote code execution vulnerability in Windows DNS Server. It carries CVSS 3.1 score 9.8, with low attack complexity and high confidentiality, integrity, and availability impact. The supplied sources do not describe the underlying weakness or exploitation method.
Likely exposure
Exposure is most likely where affected Windows Server 2008 through 2019, or listed 1909, 2004, and 20H2 releases, run the DNS Server role and remain unpatched. The bundle does not establish whether every listed system actually enables DNS services.
Exploitation context
The source bundle does not identify CVE-2021-26877 as a KEV-listed vulnerability or provide evidence of active exploitation. Its remote, unauthenticated characteristics and 9.8 score nevertheless justify urgent remediation. Do not interpret the record's recent update date as evidence of new exploitation.
Researcher notes
The available material supports severity, affected Windows Server releases, remote unauthenticated attack characteristics, and vendor patch availability. It does not supply CWE classification, root-cause details, indicators of compromise, public exploit evidence, or confirmed exploitation. Researchers should consult the current Microsoft advisory without assuming facts absent from it.
Mitigation direction
- Apply the applicable Microsoft security update identified in the vendor advisory.
- Prioritize DNS servers reachable from untrusted or broadly accessible networks.
- Follow current Microsoft guidance for affected releases, prerequisites, and deployment considerations.
- Restrict unnecessary network access to DNS servers until updates are verified.
Validation and detection
- Inventory Windows servers running the DNS Server role.
- Match operating-system releases against the affected versions in the CVE record.
- Verify installed updates against Microsoft's CVE-specific update table.
- Confirm DNS services are not unnecessarily reachable from untrusted networks.
- Avoid exploit-based validation on production DNS infrastructure.
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-2021-26877 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-2021-26877CVE 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.