SB2026090907 - Multiple vulnerabilities in Microsoft Skype for Business and Lync

Description

This security bulletin contains information about 3 vulnerabilities.

1) NULL pointer dereference (CVE-ID: CVE-2026-66303)

CWE-ID: CWE-476 - NULL Pointer Dereference

CVSSv4: 7.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to a NULL pointer dereference error in Skype for Business and Lync. A remote user can pass specially crafted data to the application and perform a denial of service (DoS) attack.

2) Out-of-bounds read (CVE-ID: CVE-2026-66308)

CWE-ID: CWE-125 - Out-of-bounds read

CVSSv4: 7.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to a boundary condition in Skype for Business and Lync. A remote user can trigger an out-of-bounds read error and cause a denial of service condition on the system.

3) Integer underflow (CVE-ID: CVE-2026-66307)

CWE-ID: CWE-191 - Integer underflow

CVSSv4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to integer underflow in Skype for Business and Lync. A remote attacker can trigger integer underflow and cause a denial of service condition on the target system.

Remediation

Install update from vendor's website.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66303
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66308
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66307