Security readout for executives and security teams
Plain-English summary
Microsoft SharePoint servers could let a low-privileged authenticated attacker execute code remotely. Because SharePoint often hosts sensitive documents and workflows, compromise can expose data and tamper with content. Attack complexity is high and the bundle shows no active exploitation evidence, but patching is urgent for exposed or business-critical farms.
Executive priority
Treat this as a high-priority SharePoint patching item, not a confirmed emergency exploitation event. Business urgency is highest where SharePoint is externally reachable, stores regulated data, or supports critical workflows.
Technical view
CVE-2021-26420 affects SharePoint Enterprise Server 2016, SharePoint Server 2019, and SharePoint Foundation 2013 SP1. CVSS 3.1 is 7.1 with network access, high attack complexity, low privileges, no user interaction, and high confidentiality and integrity impact. Microsoft classifies it as remote code execution.
Likely exposure
Organizations running affected on-premises SharePoint 2013 Foundation SP1, SharePoint Enterprise Server 2016, or SharePoint Server 2019 are potentially exposed, especially where authenticated users can reach the service over internal or external networks.
Exploitation context
The source bundle does not show CISA KEV listing or cited evidence of active exploitation. CVSS marks exploit code maturity as unproven. Exploitation requires low privileges and high complexity, so risk is serious but not presented as mass exploitation from the provided evidence.
Researcher notes
The provided data is sparse: no CWE, no exploit details, and no named mitigation beyond Microsoft advisory references. Validation should focus on exact product/version matching, patch state, authentication exposure, and whether SharePoint is reachable by broad user populations.
Mitigation direction
- Apply Microsoft’s official security update or current SharePoint guidance for CVE-2021-26420.
- Prioritize internet-facing and partner-accessible SharePoint farms first.
- Restrict SharePoint access to trusted networks where feasible.
- Review least-privilege access for SharePoint users and service accounts.
- Check vendor guidance before relying on compensating controls.
Validation and detection
- Inventory on-premises SharePoint versions and map them to affected products.
- Confirm CVE-2021-26420 security updates are installed on every SharePoint server.
- Review SharePoint exposure from internet, VPN, partner, and internal network paths.
- Check logs for unusual authenticated activity around SharePoint administrative or content operations.
- Verify backups and recovery procedures for SharePoint content databases.
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-2021-26420 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
- 7.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L/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:H/PR:L/UI:N/S:U/C:H/I:H/A:L/E:U/RL:O/RC:C1.65.5Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.1HighVector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L/E:U/RL:O/RC:C
Source materials
- CVE List V5 sourceCVE List V5
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26420CVE reference · x_refsource_MISC
- https://www.zerodayinitiative.com/advisories/ZDI-21-755/CVE reference · x_refsource_MISC
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.