How severe is CVE-2026-66303?

CVE-2026-66303 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-66303 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (66th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-66303?

CVE-2026-66303 primarily affects Microsoft Skype For Business Server. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-66303?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2026-66303 published?

CVE-2026-66303 was published on 2026-09-08 and last updated on 2026-09-16.

CVE-2026-66303

CVE-2026-66303 is a medium-severity vulnerability in Microsoft Skype For Business Server with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-476.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
EPSS exploit prediction: 1% (66th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-476
Affected product: Microsoft Skype For Business Server
Published: 2026-09-08
Last modified: 2026-09-16

Description

Null pointer dereference in Skype for Business allows an authorized attacker to deny service over a network.

Frequently asked questions

What is CVE-2026-66303?: Null pointer dereference in Skype for Business allows an authorized attacker to deny service over a network.
How severe is CVE-2026-66303?: CVE-2026-66303 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-66303 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (66th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-66303?: CVE-2026-66303 primarily affects Microsoft Skype For Business Server. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-66303?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2026-66303 published?: CVE-2026-66303 was published on 2026-09-08 and last updated on 2026-09-16.

References

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

Affected products (6)

cpe:2.3:a:microsoft:skype_for_business_server:2015:cumulative_update_13:*:*:*:*:*:*
cpe:2.3:a:microsoft:skype_for_business_server:2015:cumulative_update_13_hotfix_2:*:*:*:*:*:*
cpe:2.3:a:microsoft:skype_for_business_server:2019:cumulative_update_8:*:*:*:*:*:*
cpe:2.3:a:microsoft:skype_for_business_server:2019:cumulative_update_8_hotfix1:*:*:*:*:*:*
cpe:2.3:a:microsoft:skype_for_business_server:2019:cumulative_update_8_hotfix2:*:*:*:*:*:*
cpe:2.3:a:microsoft:skype_for_business_server_subscription_edition:7.0.2046.849:*:*:*:*:*:*:*

More vulnerabilities in Microsoft Skype For Business Server

CVE-2026-66302 — Critical (CVSS 9.8): External control of file name or path in Skype for Business allows an unauthorized attacker to execute code over a…
CVE-2026-69646 — High (CVSS 8.3): Improper verification of cryptographic signature in Skype for Business allows an unauthorized attacker to perform…
CVE-2026-66307 — High (CVSS 7.5): Integer underflow (wrap or wraparound) in Skype for Business allows an unauthorized attacker to deny service over a…
CVE-2026-66304 — High (CVSS 7.5): Server-side request forgery (ssrf) in Skype for Business allows an unauthorized attacker to disclose information over a…
CVE-2023-36789 — High (CVSS 7.2): Skype for Business Remote Code Execution Vulnerability
CVE-2023-36786 — High (CVSS 7.2): Skype for Business Remote Code Execution Vulnerability

All CVEs affecting Microsoft Skype For Business Server →

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CVE-2026-67870 — Critical (CVSS 9.8): In open62541 v1.5.5, the server-side AddReferences implementation contains an incomplete validation flaw for non-local…
CVE-2026-53399 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: nfsd: release layout stid on setlease…
CVE-2026-53355 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: net: rds: clear i_sends on setup unwind The RDS…

Browse all CWE-476 (NULL Pointer Dereference) vulnerabilities →