Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability

Microsoft Exchange Server

Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution. Added to CISA KEV on 2026-04-13 (federal deadline 2026-04-27).

First seen: 13 Apr 2026
Last update: 13 Apr 2026, 12:00 UTC
Identifiers: CVE-2023-21529
Source: CISA KEV
On the menu as: Microsoft Office

Check this repository for exposure to one security incident from pwned.coffee. Report first, change nothing until I say so.

## Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability
Severity: critical, exploited in the wild. Patch status: patched.
Affected: Microsoft Exchange Server
Ids: CVE-2023-21529

Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution. Added to CISA KEV on 2026-04-13 (federal deadline 2026-04-27).

## Steps
1. This touches infrastructure (office). Look in terraform, ansible, cloud-init, Dockerfiles and docs for the product and version we run. If it isn't in the repo, say so and list what a human should check on the box.

## Report
A table: file, product or package, version in use, affected yes/no, exact fix. Then anything a human has to check outside the repo.

If you have the pwned.coffee MCP server (https://pwned.coffee/mcp), call lookup_cve("CVE-2023-21529") for the latest, and check_repo with this repo's lockfiles, Dockerfiles and workflows for a full receipt.
Sources: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529 https://nvd.nist.gov/vuln/detail/CVE-2023-21529
https://pwned.coffee/i/microsoft-exchange-server-deserialization-of-untrusted-d-cve-2023-21529

Sources

Totalone very hot coffee