# CVE-2026-21527: Microsoft Exchange Server Spoofing Vulnerability

> An attacker can spoof critical information in the Microsoft Exchange Server user interface, potentially misleading users or bypassing security checks.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N/E:U/RL:O/RC:C`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 10 Feb 2026
- **Updated:** 19 Aug 2026
- **Also known as:** GHSA-87gj-v6h3-c8p3

## What is CVE-2026-21527?

CVE-2026-21527 is a medium-severity vulnerability in Microsoft Exchange Server, published on 10 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

User interface (ui) misrepresentation of critical information in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.

Weakness: CWE-451 (User Interface (UI) Misrepresentation of Critical Information), CWE-345 (Insufficient Verification of Data Authenticity), CWE-1286 (Improper Validation of Syntactic Correctness of Input)

## Which versions are affected by CVE-2026-21527?

It affects 2 products.


Products: Microsoft Exchange Server, Microsoft Exchange Server Subscription Edition.

## How do I fix CVE-2026-21527?

No fix has been published for CVE-2026-21527 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-21527 being exploited?

There is no known exploitation of CVE-2026-21527 in the wild and no public exploit code.

## 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-2023-21529](https://insights.sbomify.com/CVE-2023-21529/): Microsoft Exchange Server Deserialization of Untrusted Data (high 8.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-21527 and fix it if it is affected.

What it is: CVE-2026-21527 is a medium-severity vulnerability in Microsoft Exchange Server, published on 10 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-21527 in the wild and no public exploit code.

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-2026-21527/ (Markdown: https://insights.sbomify.com/CVE-2026-21527/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-21527
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-21527
- OSV: https://osv.dev/vulnerability/CVE-2026-21527

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-21527/
Summaries are generated and may contain mistakes; the official description above is the record.