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CVE-2021-26422: Skype for Business and Lync Remote Code Execution Vulnerability

• Severity: medium (CVSS 6.5 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-05-11 · updated 2026-06-17

Description

Skype for Business and Lync Remote Code Execution Vulnerability

Affected products

• Microsoft Lync Server: 2013-cumulative_update_10
• Microsoft Skype for Business Server 2019 CU7: 2015-cumulative_update_11, 2019-cumulative_update_5
• Microsoft Lync Server 2013 CU10: from 8308.0 before 8308.1144 — fixed in 8308.1144
• Microsoft Skype for Business Server 2015 CU11: from 2015 CU11 before 9319.606 — fixed in 9319.606
• Microsoft Skype for Business Server 2019 CU5: from 1.0 before 2046.369 — fixed in 2046.369

How to fix

Upgrade to a fixed version: Microsoft Lync Server 2013 CU10 8308.1144; Microsoft Skype for Business Server 2015 CU11 9319.606; Microsoft Skype for Business Server 2019 CU5 2046.369. Check the vendor advisory for mitigations.

References

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26422
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26422

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