# CVE-2026-66402: FreeRDP before 3.29.0 TLS Certificate Identity Validation Bypass

> Attackers can bypass TLS server identity verification in FreeRDP by exploiting custom certificate validation logic, allowing man-in-the-middle attacks.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 Aug 2026
- **Updated:** 5 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-66402, GHSA-43hh-p3vw-hfx3, GHSA-759r-h698-g7xj, UBUNTU-CVE-2026-66402

## What is CVE-2026-66402?

CVE-2026-66402 is a critical vulnerability in Freerdp Freerdp, published on 1 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

FreeRDP before 3.29.0 (affected versions <= 3.28.0) contains multiple TLS certificate identity validation weaknesses in tls_verify_certificate(), tls_match_hostname(), and x509_utils_get_dns_names(). Because FreeRDP performs custom Common Name and DNS SAN string matching instead of using OpenSSL's length-aware identity validation APIs, it (1) truncates DNS SAN values at embedded NUL bytes (accepting e.g. 'victim.example\0.attacker.example' as 'victim.example'), (2) accepts a matching Common Name even when non-matching DNS SAN entries are present, and (3) accepts IP-literal targets via DNS/CN matching without comparing iPAddress SANs. Under a trusted or misissued certificate chain, an attacker positioned to present such a certificate can bypass server identity verification, weakening TLS server authentication.

Weakness: CWE-295 (Improper Certificate Validation)

## Which versions are affected by CVE-2026-66402?

It affects 1 product.


Products: Freerdp Freerdp.

## How do I fix CVE-2026-66402?

Upgrade to a fixed version.

## Is CVE-2026-66402 being exploited?

There is no known exploitation of CVE-2026-66402 in the wild and no public exploit code.

## Other vulnerabilities in Freerdp Freerdp

- [CVE-2021-37594](https://insights.sbomify.com/CVE-2021-37594/): Other in n/a (critical 9.8)
- [CVE-2021-37595](https://insights.sbomify.com/CVE-2021-37595/): Other in n/a (critical 9.8)
- [CVE-2026-67305](https://insights.sbomify.com/CVE-2026-67305/): FreeRDP Windows Client before 3.29.0 Heap Buffer Overflow via Cliprdr (critical 9.4)
- [CVE-2026-67289](https://insights.sbomify.com/CVE-2026-67289/): FreeRDP before 3.29.0 HTTP Proxy Request Injection via Redirection (critical 9.3)
- [CVE-2026-67292](https://insights.sbomify.com/CVE-2026-67292/): FreeRDP before 3.29.0 WebSocket Ping Buffer Over-disclosure (critical 9.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-66402 and fix it if it is affected.

What it is: CVE-2026-66402 is a critical vulnerability in Freerdp Freerdp, published on 1 Aug 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-2026-66402 in the wild and no public exploit code.

Affected product: Freerdp Freerdp. 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-2026-66402/ (Markdown: https://insights.sbomify.com/CVE-2026-66402/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-66402
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-66402
- OSV: https://osv.dev/vulnerability/CVE-2026-66402

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-66402/
Summaries are generated and may contain mistakes; the official description above is the record.