CVE-2026-55009Important
Microsoft Exchange Server Elevation of Privilege Vulnerability
Assessment
Deserialization of untrusted data in Microsoft Exchange Server allows an authorized attacker to elevate privileges locally.
- Severity
- Important
- CVSS base score
- 7.8CVSS:3.1/
AV:L/ AC:L/ PR:L/ UI:N/ S:U/ C:H/ I:H/ A:H/ E:U/ RL:O/ RC:C - Impact
- Elevation of Privilege
- EPSS, next 30 days
- 2.5%Higher than 84.2% of scored CVEs · FIRST model run 26 Sep 2026 · about EPSS
- Exploitability
- Exploitation Unlikely
- Publicly disclosed
- No
- Customer action
- Required: apply the update
- Component
- Microsoft Exchange Server
- Weakness
- CWE-502: Deserialization of Untrusted Data
- Issued by
- Microsoft
- Published
- 14 Jul 2026 · July 2026
- Last revised
- 14 Jul 2026
Updates that fix it
4 KBs| KB | Type | Restart | Applies to | Other CVEs |
|---|---|---|---|---|
| KB5103212 | Security Update | Required | Microsoft Exchange Server Subscription Edition RTM | All CVEs in KB5103212 |
| KB5103213 | Security Update | Required | Microsoft Exchange Server 2019 Cumulative Update 15 | All CVEs in KB5103213 |
| KB5103214 | Security Update | Required | Microsoft Exchange Server 2019 Cumulative Update 14 | All CVEs in KB5103214 |
| KB5103215 | Security Update | Required | Microsoft Exchange Server 2016 Cumulative Update 23 | All CVEs in KB5103215 |
Affected products
ESU, Server Software4 affected products
- Microsoft Exchange Server 2016 Cumulative Update 23
- Microsoft Exchange Server 2019 Cumulative Update 14
- Microsoft Exchange Server 2019 Cumulative Update 15
- Microsoft Exchange Server Subscription Edition RTM