CVE-2026-55009
Microsoft Exchange Server Elevation of Privilege Vulnerability
No known exploitation. EPSS puts it in the 85th percentile. Fixed versions are out.
What to do
Find your product and version, then upgrade to the build on the right.
- Microsoft Exchange Server 2016 Cumulative Update 23Affected: ≥ 15.01.0.0, < 15.01.2507.071Upgrade to: 15.01.2507.071Stated by: CVE record
- Microsoft Exchange Server 2019 Cumulative Update 14Affected: ≥ 15.02.0.0, < 15.02.1544.043Upgrade to: 15.02.1544.043Stated by: CVE record
- Microsoft Exchange Server 2019 Cumulative Update 15Affected: ≥ 15.02.0.0, < 15.02.1748.048Upgrade to: 15.02.1748.048Stated by: CVE record
- Microsoft Exchange Server Subscription Edition RTMAffected: ≥ 15.02.0.0, < 15.02.2562.045Upgrade to: 15.02.2562.045Stated by: CVE record
- Microsoft Exchange Server Subscription EditionAffected: < 15.02.2562.045Upgrade to: 15.02.2562.045Stated by: NVD
Versions as the sources state them. Full version matrix after sign-in
What it is
From the CVE record
Deserialization of untrusted data in Microsoft Exchange Server allows an authorized attacker to elevate privileges locally.
In plain language
No plain-language summary for this CVE yet.
Exploitation
Where each signal puts this CVE on the scale from published to confirmed exploited.
- CISA KEV
Not in the catalog. CISA has not confirmed exploitation.
- Public exploits
No public exploit or proof of concept found in the sources we track.
- EPSS
2.5% chance of exploitation activity in the next 30 days, which ranks it in the 85th percentile of scored CVEs.
Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.
Lifecycle
9 events over 10 days, from the signal feeds we watch.
- Patch availablerecord updated
- OpenVAS check added
- Record updated
- Publishedweakness classified, att&ck mapped, record updated, record updated
Affected products
- Microsoft Exchange Server 2016 Cumulative Update 23Operating Systems
- Microsoft Exchange Server 2019 Cumulative Update 14Operating Systems / windows
- Microsoft Exchange Server 2019 Cumulative Update 15Enterprise Software / itsm-monitoring
- Microsoft Exchange Server Subscription Edition RTMEnterprise Software / itsm-monitoring
- exchange serverOperating Systems / windows
- exchange server subscription editionEnterprise Software / itsm-monitoring
Technical detail
CVSS 3.1 vector
Open in the CVSS calculatorCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Scored 7.8 by NVD.
How it is reached
- Attack Vector LocalRequires local access to the vulnerable system (e.g. local login, malicious file)
- Attack Complexity LowNo special conditions — the attack can be reliably reproduced
- Privileges Required LowRequires basic user-level privileges
- User Interaction NoneNo user interaction needed — fully automated exploitation
Scope
- Scope UnchangedImpact is limited to the vulnerable component itself
Impact if exploited
- Confidentiality HighTotal information disclosure — all data in the component is compromised
- Integrity HighTotal loss of integrity — attacker can modify any data in the component
- Availability HighTotal denial of service — the component is completely unavailable
Weaknesses
ATT&CK techniques
Mapped from the weaknesses above (CWE to ATT&CK), not observed in attacks.
Sources
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