# CVE-2026-56766: Hydra - Stack Buffer Overflow in NTLM Authentication Handler

> A malicious server can trigger a stack buffer overflow in Hydra's NTLM handler, potentially allowing remote code execution on the client system.

- **Severity:** High 8.6 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/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:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 25 Jun 2026
- **Updated:** 14 Jul 2026
- **Also known as:** GHSA-3r6x-6cp5-6575, UBUNTU-CVE-2026-56766, openSUSE-SU-2026:11131-1

## What is CVE-2026-56766?

CVE-2026-56766 is a high-severity memory corruption vulnerability in vanhauser-thc thc-hydra, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Hydra through 9.7, fixed in commit 9cc84c2, contains a stack buffer overflow in NTLM authentication across SMTP, POP3, IMAP, NNTP, HTTP, HTTP-Proxy, and HTTP-Proxy-Urlenum modules when processing malicious NTLM Type-2 challenges. A malicious server can send a crafted NTLM Type-2 challenge with an excessively long domain string, causing base64-encoded response data to overflow a 500-byte stack buffer by 18 to 330 bytes, enabling remote code execution on systems without stack protection.

Weakness: CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2026-56766?


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hydra` | openSUSE:Tumbleweed | All versions | 9.7+git20.gbccaea1-1.1 |

## How do I fix CVE-2026-56766?

Apply the vendor's patch.

## Is CVE-2026-56766 being exploited?

There is no known exploitation of CVE-2026-56766 in the wild and no public exploit code.

Public exploit code:

- Hydra - Stack Buffer Overflow (exploitdb)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-56766 and fix it if it is affected.

What it is: CVE-2026-56766 is a high-severity memory corruption vulnerability in vanhauser-thc thc-hydra, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-56766 in the wild and no public exploit code.

Affected product: vanhauser-thc thc-hydra. 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-2026-56766/ (Markdown: https://insights.sbomify.com/CVE-2026-56766/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-56766
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-56766
- OSV: https://osv.dev/vulnerability/CVE-2026-56766

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-56766/
Summaries are generated and may contain mistakes; the official description above is the record.