# CVE-2023-21529: Microsoft Exchange Server Deserialization of Untrusted Data

> Attackers can execute arbitrary code on Microsoft Exchange Server via a deserialization vulnerability, requiring immediate patching.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C`)
- **Exploited in the wild:** Yes, since 13 Apr 2026 (CISA KEV), used in ransomware
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Feb 2023
- **Updated:** 19 Aug 2026
- **Also known as:** GHSA-hjxr-gv9h-rjxc

## What is CVE-2023-21529?

CVE-2023-21529 is a high-severity unsafe deserialization vulnerability in Microsoft Exchange Server, published on 14 Feb 2023. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Microsoft Exchange Server Remote Code Execution Vulnerability

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2023-21529?

It affects 1 product.


Products: Microsoft Exchange Server.

## How do I fix CVE-2023-21529?

No fix has been published for CVE-2023-21529 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 27 Apr 2026.

## Is CVE-2023-21529 being exploited?

Yes. Attackers have exploited CVE-2023-21529 in the wild since at least 13 Apr 2026, including in ransomware campaigns.

## Other vulnerabilities in Microsoft Exchange Server

- [CVE-2024-21410](https://insights.sbomify.com/CVE-2024-21410/): Microsoft Exchange Server Privilege Escalation (critical 9.8, exploited in the wild)
- [CVE-2021-34473](https://insights.sbomify.com/CVE-2021-34473/): Microsoft Exchange Server Remote Code Execution (critical 9.1, exploited in the wild)
- [CVE-2021-26855](https://insights.sbomify.com/CVE-2021-26855/): Microsoft Exchange Server Remote Code Execution (critical 9.1, exploited in the wild)
- [CVE-2021-34523](https://insights.sbomify.com/CVE-2021-34523/): Microsoft Exchange Server Privilege Escalation (critical 9.0, exploited in the wild)
- [CVE-2022-41080](https://insights.sbomify.com/CVE-2022-41080/): Microsoft Exchange Server Privilege Escalation (high 8.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-21529 and fix it if it is affected.

What it is: CVE-2023-21529 is a high-severity unsafe deserialization vulnerability in Microsoft Exchange Server, published on 14 Feb 2023. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2023-21529 in the wild since at least 13 Apr 2026, including in ransomware campaigns.

Affected product: Microsoft Exchange Server. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2023-21529/ (Markdown: https://insights.sbomify.com/CVE-2023-21529/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-21529
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-21529
- OSV: https://osv.dev/vulnerability/CVE-2023-21529

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-21529/
Summaries are generated and may contain mistakes; the official description above is the record.