Microsoft Exchange Server: Elevation of privilege via weak authentication
Summary
Microsoft Exchange Server Subscription Edition (SE) RTM contains a weak authentication flaw (CWE-1390). An attacker who already holds high privileges on the network can use it to elevate privileges further. Exploitation therefore requires an existing high-privileged account, such as an administrator. Microsoft rates exploitation as less likely, and the sources reviewed report no public proof-of-concept and no in-the-wild exploitation.
Affected
- Microsoft Exchange Server Subscription Edition RTM (x64): 15.02.0.0 before 15.02.2562.057
- Exchange Server 2016 and 2019: no fix is provided for this CVE
Fixed in
- Exchange Server SE: build 15.02.2562.057 or later (cumulative update SU12, KB5133453, per a secondary source)
Workaround
Unknown. No workaround is documented in the sources reviewed. Apply the security update.
Exploitation
- Microsoft exploitability assessment: Exploitation Less Likely, not publicly disclosed (per Rapid7 table)
- CISA SSVC in the CVE record: Exploitation none, Automatable no, Technical Impact total
- No in-the-wild exploitation reported in the sources reviewed
- CISA KEV status not verified directly
- No public proof-of-concept found
Our recommendation
- Install the November 2026 Exchange SE security update (SU12, build 15.02.2562.057 or later) and run the Exchange Health Checker afterwards.
- Verify that no Exchange 2016 or 2019 servers remain and plan a migration to SE for legacy systems.
- Review administrator accounts, enforce multi-factor authentication for privileged accounts and review the Exchange admin audit logs.
- Priority is moderate because high privileges are required; include the fix in the regular cumulative update cycle.
Information from Microsoft (Patch Tuesday November 2026)
- Severity (Microsoft)
- Important
- Impact
- Elevation of privilege – Microsoft Exchange Server
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Server software (Exchange, SharePoint …)
- Updates (KB)
- KB5133453
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Response Center: CVE-2026-118157 msrc.microsoft.com
- CVE Record: CVE-2026-118157 www.cve.org
- Microsoft Exchange Team: November 2026 Exchange Server Security Updates techcommunity.microsoft.com
- Rapid7: Patch Tuesday November 2026 www.rapid7.com
- Icewolf: Exchange Server SE SU12 released (secondary) blog.icewolf.ch
- Microsoft Exchange Team: Period 2 Exchange 2016/2019 ESU program techcommunity.microsoft.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 11 Nov 2026, 06:46.
Original description (NVD)
Weak authentication in Microsoft Exchange Server allows an authorized attacker to elevate privileges over a network.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.