Security readout for executives and security teams
Plain-English summary
CVE-2021-26418 is a Microsoft SharePoint spoofing vulnerability. The supplied scoring indicates an attacker needs low privileges and user interaction, with limited confidentiality and integrity impact and no availability impact. It is important for organizations running affected SharePoint versions, but the available sources do not support emergency treatment.
Executive priority
Treat this as a scheduled remediation item, not a crisis, unless affected SharePoint systems are externally exposed or protect sensitive data. The main business risk is user deception or trust abuse inside SharePoint workflows, not service outage.
Technical view
The issue is classified as CWE-290 and affects SharePoint Foundation 2013 SP1, SharePoint Enterprise Server 2016, and SharePoint Server 2019. The CVSS 3.1 vector is AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N, scored 4.6. Microsoft lists official remediation as available in the supplied vector metadata.
Likely exposure
Exposure is most likely in organizations still operating affected on-premises SharePoint versions, especially internet-accessible or broadly reachable deployments. The source bundle does not identify SharePoint Online or other Microsoft products as affected.
Exploitation context
The bundle does not report active exploitation, and the KEV flag is false. The CVSS temporal signal marks exploit maturity as unproven. Exploitation requires an authenticated attacker and user interaction, reducing urgency compared with unauthenticated remote code execution issues.
Researcher notes
Public detail in the supplied bundle is sparse. The strongest technical facts are the affected products, CWE-290 classification, Microsoft advisory reference, and CVSS vector. Do not assume exploitability beyond authenticated network access plus user interaction without additional vendor detail.
Mitigation direction
- Review the Microsoft MSRC advisory for the applicable security update.
- Apply official Microsoft SharePoint security updates for affected versions.
- Prioritize externally reachable SharePoint farms and high-value collaboration portals.
- Reduce unnecessary SharePoint exposure while remediation is planned.
- Confirm unsupported or legacy SharePoint deployments have a retirement or isolation plan.
Validation and detection
- Inventory SharePoint Foundation 2013 SP1, SharePoint 2016, and SharePoint 2019 instances.
- Compare installed build and patch levels against Microsoft guidance for CVE-2021-26418.
- Confirm no affected unpatched SharePoint servers remain reachable from untrusted networks.
- Check vulnerability scanner results for this CVE after patching.
- Document compensating controls where immediate patching is not possible.
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-290: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. 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 lookupCVE-2021-26418 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
- Medium
- CVSS
- 4.6 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N/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:L/UI:R/S:U/C:L/I:L/A:N/E:U/RL:O/RC:C2.12.5Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
4.6MediumVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N/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-2021-26418CVE 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.
Authentication Bypass by Spoofing
Authentication Bypass by Spoofing represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.