Security readout for executives and security teams
Plain-English summary
A flaw in supported on-premises Microsoft SharePoint server products can let a user who already has some authorized access run malicious code remotely. Successful exploitation could expose, alter, or disrupt SharePoint data and services. CISA’s KEV listing indicates exploitation has occurred in the wild.
Executive priority
Treat this as an immediate remediation priority because exploitation is recognized by CISA and successful compromise could materially affect sensitive content and service availability. Establish affected-server ownership, patch promptly, verify complete farm coverage, and investigate potentially exposed systems. The evidence supports urgency but not assumptions that every SharePoint environment is compromised.
Technical view
CVE-2026-45659 is an untrusted-data deserialization vulnerability (CWE-502). It is network reachable, requires low privileges, needs no user interaction, and has low attack complexity. Successful exploitation can provide high confidentiality, integrity, and availability impact. The supplied CVSS 3.1 score is 8.8.
Likely exposure
Potential exposure includes Microsoft SharePoint Enterprise Server 2016, SharePoint Server 2019, and SharePoint Server Subscription Edition deployments identified in the source bundle. Internet-accessible or broadly reachable servers deserve first attention. The bundle does not establish that SharePoint Online or other Microsoft products are affected.
Exploitation context
CISA KEV status supports known exploitation. The supplied sources do not describe exploitation scale, targeted organizations, attacker groups, indicators, public proof-of-concept availability, or attack chains. Exploitation still requires an authorized, low-privileged attacker account or equivalent access.
Researcher notes
The weakness is CWE-502 with AV:N/AC:L/PR:L/UI:N/S:U and high impact across confidentiality, integrity, and availability. Exact vulnerable build ranges, serialization entry points, exploitation artifacts, and patch mechanics are absent from the bundle. Researchers should rely on Microsoft’s advisory for build-level applicability and avoid extrapolating exposure to unlisted products.
Mitigation direction
- Apply Microsoft’s security update for CVE-2026-45659 to every affected SharePoint server.
- Follow the Microsoft advisory for prerequisites, installation sequencing, and any required post-update actions.
- Prioritize externally reachable and business-critical SharePoint deployments.
- If patching is delayed, consult Microsoft guidance for supported temporary mitigations.
Validation and detection
- Inventory on-premises SharePoint products, editions, server roles, and installed build numbers.
- Compare each build and update level with Microsoft’s CVE advisory.
- Confirm the security update is installed successfully across every server in each SharePoint farm.
- Review SharePoint, authentication, web, and endpoint telemetry for suspicious activity around privileged application processes.
- Use vendor-provided indicators if Microsoft or CISA publishes them; none are supplied here.
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-2026-45659 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
- Yes
- 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.
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: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.
- Added to KEVCISA-ADP
CISA Known Exploited Vulnerabilities metadata lists this CVE as known exploited.
- ADP timelineCISA-ADP
CVE-2026-45659 added to CISA KEV
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
- 2026-07-01T00:00:00.000Z: CVE-2026-45659 added to CISA KEV
Source materials
- CVE List V5 sourceCVE List V5
- Microsoft SharePoint Remote Code Execution VulnerabilityCVE reference, microsoft · vendor-advisory, patch
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-45659CVE 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.
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.