Microsoft Bookings: Authorization bypass through user-controlled key
Summary
Microsoft Bookings, a cloud service for online scheduling and customer bookings in Microsoft 365, contains an authorization bypass caused by a user-controlled key (CWE-639). An unauthenticated attacker on the network can exploit it to elevate privileges, with a changed scope and high integrity impact according to the CVSS vector. Microsoft applies the fix on its own service, so customers have no patch to install.
Affected
- Microsoft Bookings (cloud service in Microsoft 365)
- Exact affected service versions: Unknown.
Fixed in
- Fixed server-side by Microsoft, released October 8, 2026.
- Customer action: none required according to Microsoft.
- Exact fix timestamp: Unknown.
Workaround
- No customer-side workaround documented by Microsoft.
- Generic measure: review application and audit logs for privilege changes or access by low-privilege users.
Exploitation
- Microsoft's exploitability assessment: not exploited at publication; exploit code maturity "Unproven".
- Public proof of concept: Unknown.
- CISA KEV listing: Unverified.
Our recommendation
- Check whether Microsoft Bookings is enabled in your Microsoft 365 tenant.
- Review Bookings-related audit logs and admin or staff role changes from October 2026 onward.
- Limit Microsoft 365 admin roles and confirm the Microsoft Service Health dashboard shows no open incident.
- Monitor Microsoft's advisory and CISA KEV for changes in exploitation status.
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- MSRC Security Update Guide (CVE record) msrc.microsoft.com
- MSRC Advisory CVE-2026-94510 msrc.microsoft.com
- TheHackerWire CVE-2026-94510 analysis www.thehackerwire.com
- NVD/CIRCL record via Vulners vulners.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 30 Oct 2026, 15:35.
Original description (NVD)
Authorization bypass through user-controlled key in Microsoft Bookings allows an unauthorized 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.
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