CVE-2026-45659: Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability
What it is
Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network.
What to do
Treat this as urgent. Identify every affected system, starting with anything internet-facing, and apply the vendor fix or mitigation within days. If you cannot patch quickly, isolate or disable the affected service and watch for signs of compromise.
- Priority
- Act now: Patch or mitigate internet-facing systems within days.
- Severity (CVSS)
- 8.8 high
- CISA assessment (SSVC)
- actively exploited; needs manual effort per target; total control of the affected system
- Exploit probability (EPSS, 30 days)
- 2.7%, higher than 85% of all CVEs
- Added to CISA KEV
- 1 July 2026
- CISA fix-by date
- 4 July 2026 (US federal agencies; a sensible deadline for everyone)
- Ransomware use
- Known
- Weakness
- CWE-502
References
- NIST NVD entry
- CISA KEV entry
- msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45659
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-45659
Sources: CISA Known Exploited Vulnerabilities · FIRST Exploit Prediction Scoring System (EPSS) · NIST National Vulnerability Database · CISA Vulnrichment (SSVC), via the CVE Program. This product uses data from the NVD API but is not endorsed or certified by the NVD. Summaries are machine-written from CISA’s description; treat the vendor’s advisory as the authority for fixes.