Microsoft Exchange Server: Spoofing vulnerability via improper access control
Summary
An improper access control flaw in Microsoft Exchange Server Subscription Edition allows an authenticated attacker to perform spoofing over the network. The CVSS score is 7.1 (High), with impact on integrity and availability and no confidentiality impact. The attacker needs a valid low-privilege account, and no user interaction is required.
Affected
- Microsoft Exchange Server Subscription Edition RTM (on-premises)
- Versions from 15.02.0.0 before 15.02.2562.057 (per the CVE record; fixed build to be verified in the MSRC advisory)
- Older Exchange versions are not listed as affected in the CVE record. Exchange Online: Unknown.
Fixed in
- Security update for Exchange Server Subscription Edition RTM, build 15.02.2562.057 or later (per third-party tracker; verify in the MSRC advisory)
- KB number: Unknown. Check the MSRC advisory.
Workaround
- Unknown. No workaround or mitigation has been published for this CVE. Applying the security update is the remedy.
Exploitation
- Rapid7 rates exploitation as less likely and reports no public disclosure.
- CISA SSVC: Exploitation none, not automatable.
- CVSS temporal vector: Exploit maturity Unproven, Report confidence Confirmed.
- No public proof of concept and no confirmed in-the-wild exploitation found.
- KEV status: Not listed according to a third-party tracker; verify in the CISA catalogue.
Our recommendation
- Identify on-premises Exchange Server Subscription Edition systems and check their build number.
- Install the Microsoft security update from the MSRC advisory as soon as possible and verify the build is at or above 15.02.2562.057.
- Plan migration away from unsupported on-premises Exchange versions.
- Monitor mailbox and authentication logs for unusual spoofed messages or account misuse.
- Priority: medium-high for on-premises Exchange Subscription Edition; low for Exchange Online and Microsoft 365.
Information from Microsoft (Patch Tuesday November 2026)
- Severity (Microsoft)
- Important
- Impact
- Spoofing – 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 Update Guide: CVE-2026-118208 msrc.microsoft.com
- CVE Record CVE-2026-118208 www.cve.org
- Rapid7 Patch Tuesday November 2026 (Exchange) www.rapid7.com
- Rapid7 Exchange Patch Tuesday November 2026 www.rapid7.com
- Strix AI: CVE-2026-118208 www.strix.ai
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, 07:12.
Original description (NVD)
Improper access control in Microsoft Exchange Server allows an authorized attacker to perform spoofing 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.
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