CVE-2021-26422Network attack vector

Authenticated remote code execution

Published May 11, 2021 · Updated Aug 3, 2024

Remote code execution in Microsoft Skype for Business and Lync Server versions listed below allows remote authenticated users to execute code through network requests. Microsoft has not published the vulnerable component or specific input-handling operation, so the mechanism remains undisclosed in the available advisory record. The CVSS record requires high privileges and no user interaction; successful exploitation can compromise confidentiality, integrity, and availability.

CVSS severity7.2
High
EPSS probability2.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Remote code execution in Microsoft Skype for Business and Lync Server versions listed below allows remote authenticated users to execute code through network requests. Microsoft has not published the vulnerable component or specific input-handling operation, so the mechanism remains undisclosed in the available advisory record. The CVSS record requires high privileges and no user interaction; successful exploitation can compromise confidentiality, integrity, and availability.

The record

CVE
CVE-2021-26422
Published
May 11, 2021
Updated
Aug 3, 2024
Vendor
Microsoft
Product
Microsoft Skype for Business Server 2015
Classifications
Unavailable
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 11, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2015 CU11 <9319.606

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Microsoft · Microsoft Skype for Business Server 2015version=2015 CU11 <9319.606
Microsoft · Microsoft Skype for Business Server 2019version=1.0 <2046.369
Microsoft · Microsoft Lync Server 2013version=8308.0 <8308.1144

Published CVSS scores

6.5NVDAV:N/AC:L/Au:S/C:P/I:P/A:P
7.2MicrosoftCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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