CVE-2026-85873: CWE-639: Authorization Bypass Through User-Controlled Key in Microsoft Skype for Business Server 2015 CU13
Description
CVE-2026-85873 is an authorization bypass vulnerability in Microsoft Skype for Business Server 2015 CU13 that allows an authorized attacker to elevate privileges over a network. The flaw involves improper authorization related to user-controlled keys. This vulnerability has a medium severity rating with a CVSS score of 6.5. An official fix is available from Microsoft.
CVSS v3.1
Score 6.5medium
Affected software
Microsoft
Skype for Business Server 2015 CU13
Microsoft
Skype for Business Server 2019 CU8
Microsoft
Skype for Business Server Subscription Edition CU1
Microsoft
Skype for Business Server Subscription Edition RTM
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability (CVE-2026-85873) in Microsoft Skype for Business Server 2015 CU13 is caused by improper authorization, specifically CWE-639: Authorization Bypass Through User-Controlled Key. It allows an attacker who is already authorized on the network to elevate their privileges by exploiting the flaw in the authorization mechanism. The vulnerability affects multiple version ranges of the product as specified. Microsoft has published an official fix to address this issue.
Potential Impact
An authorized attacker can exploit this vulnerability to elevate their privileges within the Skype for Business Server environment. This could lead to unauthorized access to sensitive information or functionality that should be restricted. The vulnerability does not impact confidentiality beyond the elevated privileges, nor does it affect availability or integrity directly. No known exploits are currently reported in the wild.
Mitigation Recommendations
Microsoft has released an official fix for this vulnerability. Users of Skype for Business Server 2015 CU13 should apply the provided security update as soon as possible to remediate the issue. Since an official fix is available, no additional mitigation steps are required beyond patching.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- microsoft
- Date Reserved
- 2026-09-04T18:18:19.324Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- official-fix
- Vendor Advisory Urls
- [{"url":"https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-85873","vendor":"Microsoft"}]
Threat ID: 6ace85482cdf04f6569fec61
Added to database: 10/13/2026, 19:23:52 UTC
Last enriched: 10/14/2026, 02:49:58 UTC
Last updated: 10/14/2026, 02:49:58 UTC
Views: 2
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