CVE-2026-45659
Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability
Microsoft SharePoint Server
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
Ransomware groups exploiting CVE-2026-45659
The Warlock ransomware and operator(s) are believed to be attributed to Storm-2603, a China-based threat actor who is also known to have deployed LockBit ransomware. There's also a crossover between victims with Black Basta. Both are RaaS and have a long list
Exploitation is attributed to these groups across their recorded activity. It does not follow that every organisation they listed was reached through CVE-2026-45659 — the source data does not record an entry point per incident.
Exploitation status
CISA Known Exploited Vulnerabilities
Listed by CISA on 1 July 2026. US federal agencies were required to remediate it by 4 July 2026. CISA records this vulnerability as known to be used in ransomware campaigns.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 2.7%, which is higher than 85.7% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Recent listings by these groups
Disclosures from the groups above, newest first.
Frequently asked questions
Is CVE-2026-45659 being exploited by ransomware groups?
Yes. CVE-2026-45659 is recorded as exploited by Warlock. Between them these groups account for 78 victim disclosures in this database. CISA also records this vulnerability as used in ransomware campaigns.
What does CVE-2026-45659 affect?
CVE-2026-45659 affects Microsoft SharePoint Server. Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
How severe is CVE-2026-45659?
CVE-2026-45659 is rated HIGH with a CVSS base score of 8.8. EPSS puts the probability of exploitation in the next 30 days at 2.7%, higher than 85.7% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 4 July 2026.
How should organisations respond to CVE-2026-45659?
Apply the vendor patch for Microsoft SharePoint Server as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.