Security readout for executives and security teams
Plain-English summary
A signed-in attacker with limited privileges could exploit unsafe data handling in affected SharePoint Server deployments and run code remotely. Successful exploitation could expose documents, alter content, disrupt service, or compromise the underlying server. The supplied record rates the vulnerability 8.8 High.
Executive priority
Treat as a high-priority patching issue. The need for an authorized account reduces immediate exposure, but low-complexity remote code execution could enable complete server compromise. Expedite remediation for externally reachable, business-critical, or sensitive-data SharePoint farms.
Technical view
CVE-2026-40357 is a CWE-502 deserialization vulnerability in Microsoft Office SharePoint. Its CVSS 3.1 vector indicates network access, low complexity, low privileges, no user interaction, unchanged scope, and high confidentiality, integrity, and availability impact.
Likely exposure
Exposure is limited by the stated requirement for an authorized attacker, but remains significant where affected SharePoint servers are accessible to many users or compromised accounts. The bundle lists SharePoint Enterprise Server 2016, Server 2019, and Subscription Edition, each identified as version 16.0.0.
Exploitation context
The supplied bundle does not identify active exploitation, and CVE-2026-40357 is not marked as KEV. Exploit maturity is recorded as unproven. This does not establish that exploitation is impossible; it means public evidence supplied here is insufficient to claim exploitation.
Researcher notes
The CVSS vector is AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. The underlying weakness is untrusted-data deserialization. The source bundle does not describe the vulnerable component, attack path, prerequisites beyond authorization, indicators of compromise, or specific update identifiers; consult Microsoft’s advisory for those details.
Mitigation direction
- Review Microsoft’s CVE advisory and apply the vendor-provided security update for each affected SharePoint deployment.
- Prioritize internet-accessible or broadly accessible SharePoint servers and systems holding sensitive documents.
- Restrict SharePoint access to necessary users and trusted networks until updates are confirmed.
- Monitor Microsoft guidance for revised affected-version details or additional mitigations.
Validation and detection
- Inventory SharePoint Enterprise Server 2016, Server 2019, and Subscription Edition installations.
- Compare installed build and update levels with Microsoft’s CVE advisory.
- Confirm every SharePoint server in each farm received the applicable update.
- Review authentication and server telemetry for unusual activity by authorized or compromised accounts.
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-502: Code execution behavior lookup
Code execution and unsafe deserialization weaknesses often justify reviewing execution behavior and process 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-2026-40357 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
- 8.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/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.
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:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C2.85.9microsoftVulnerability scoring details
Base CVSS 3.1 score
8.8HighVector: CVSS:3.1/AV:N/AC:L/PR:L/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
- Microsoft SharePoint Server Remote Code Execution VulnerabilityCVE reference, microsoft · vendor-advisory, patch
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.
Deserialization of Untrusted Data
Deserialization of Untrusted Data represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.