Security readout for executives and security teams
Plain-English summary
CVE-2021-27065 is a high-severity Microsoft Exchange Server vulnerability that can enable remote code execution. Successful exploitation could compromise email confidentiality, integrity, and availability. CISA lists it as known exploited, making unsupported or unpatched affected Exchange servers an urgent business risk.
Executive priority
Treat as immediate. Confirm inventory, patch affected Exchange servers, and investigate previously exposed systems. Because exploitation is documented, leaders should track remediation and compromise assessment separately, with accountable owners and deadlines.
Technical view
The vulnerability is classified as path traversal (CWE-22) and remote code execution, with CVSS 3.1 score 7.8. The supplied vector indicates low complexity, no privileges, required user interaction, and local attack vector. Affected entries cover specified Exchange Server 2013, 2016, and 2019 releases. The bundle does not document exploitation mechanics or required chaining.
Likely exposure
Exposure is limited to organizations operating the listed on-premises Microsoft Exchange Server 2013, 2016, or 2019 releases and cumulative updates. Determine exposure from exact installed versions and update status. The supplied evidence does not establish exposure for products or versions absent from the affected list.
Exploitation context
CISA's Known Exploited Vulnerabilities listing confirms exploitation in the wild. The bundle does not specify campaign recency, prevalence, indicators, attacker identities, or whether exploitation required another vulnerability. Do not treat patching alone as evidence that previously exposed systems were never compromised.
Researcher notes
The evidence supports affected Exchange releases, CWE-22, high severity, patch availability, and known exploitation. It does not supply KB identifiers, file paths, indicators, exploitation chronology, or chain dependencies. Validate those details directly against the current Microsoft advisory before detection engineering or incident-scoping decisions.
Mitigation direction
- Apply Microsoft's security update for CVE-2021-27065 following vendor guidance.
- Prioritize listed Exchange servers that remain unpatched or unsupported.
- Restrict access to affected servers until updates and investigation are complete.
- Review current Microsoft guidance for prerequisites and supported upgrade paths.
Validation and detection
- Inventory Exchange Server editions, cumulative updates, and build numbers.
- Compare every installed build against Microsoft's CVE advisory and affected list.
- Verify the relevant security update installed successfully on each affected server.
- Investigate previously exposed systems using current Microsoft and CISA guidance.
- Document systems proven unaffected, remediated, isolated, or pending action.
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.
CWE-22: File access and web shell behavior lookup
File traversal and upload weaknesses can lead teams to review file, web shell, execution, and collection telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution 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-2021-27065 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
- High
- CVSS
- 7.8 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/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.
CISA KEV status
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:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C1.85.9microsoftVulnerability scoring details
Base CVSS 3.1 score
7.8HighVector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/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.
- Added to KEVCISA-ADP
CISA Known Exploited Vulnerabilities metadata lists this CVE as known exploited.
- ADP timelineCISA-ADP
CVE-2021-27065 added to CISA KEV
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
- 2021-11-03T00:00:00.000Z: CVE-2021-27065 added to CISA KEV
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-2021-27065CVE reference, CVE · x_refsource_MISC, x_transferred
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27065CVE reference, CISA-ADP · government-resource
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.