# CVE-2026-28221: Wazuh: Pre-auth stack-based buffer overflow in wazuh-remoted print_hex_string() due to signed char promotion on x86_64

> Remote attackers can trigger a stack-based buffer overflow in Wazuh's unauthenticated TCP service, potentially leading to code execution or denial of service.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 29 Apr 2026
- **Updated:** 29 Apr 2026
- **Also known as:** GHSA-q9vv-7w4c-f4cm

## What is CVE-2026-28221?

CVE-2026-28221 is a medium-severity memory corruption vulnerability in Wazuh Wazuh, published on 29 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Wazuh is a free and open source platform used for threat prevention, detection, and response. From version 4.8.0 to before version 4.14.4, a stack-based buffer overflow exists in print_hex_string() in wazuh-remoted. The bug is triggered when formatting attacker-controlled bytes using sprintf(dst_buf + 2*i, "%.2x", src_buf[i]) on platforms where char is treated as signed and the compiled code sign-extends bytes before the variadic call. For input bytes such as 0xFF, the formatting can emit "ffffffff" (8 chars) instead of "ff" (2 chars), causing an out-of-bounds write past a fixed 2049-byte stack buffer. The vulnerable path is reachable remotely prior to any agent authentication/registration logic via TCP/1514 when an oversized length prefix causes the “unexpected message (hex)” diagnostic path to run. Additionally, the same unauthenticated oversized-message diagnostic path logs an attacker-controlled hex dump to /var/ossec/logs/ossec.log for each trigger, allowing remote log amplification that can degrade monitoring fidelity and consume disk/I/O. This log amplification is reachable even without triggering the sign-extension overflow (e.g., using bytes < 0x80). This issue has been patched in version 4.14.4.

Weakness: CWE-400 (Uncontrolled Resource Consumption), CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2026-28221?

It affects 1 product.


Products: Wazuh Wazuh.

## How do I fix CVE-2026-28221?

No fix has been published for CVE-2026-28221 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-28221 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-28221 exists.

## Other vulnerabilities in Wazuh Wazuh

- [CVE-2025-24016](https://insights.sbomify.com/CVE-2025-24016/): Wazuh Server Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2024-32038](https://insights.sbomify.com/CVE-2024-32038/): Wazuh Analysis Engine Event Decoder Heap-based Buffer Overflow Remote Code Execution Vulnerability (critical 9.8)
- [CVE-2021-44079](https://insights.sbomify.com/CVE-2021-44079/): Command injection in n/a (critical 9.8)
- [CVE-2024-1243](https://insights.sbomify.com/CVE-2024-1243/): Remote code execution and local privilege escalation in Wazuh Windows agent via NetNTLMv2 hash theft (critical 9.5)
- [CVE-2026-61800](https://insights.sbomify.com/CVE-2026-61800/): Wazuh cluster worker file sync allows arbitrary file write under /var/ossec (incomplete fix for CVE-2026-30893) (critical 9.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-28221 and fix it if it is affected.

What it is: CVE-2026-28221 is a medium-severity memory corruption vulnerability in Wazuh Wazuh, published on 29 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-28221 exists.

Affected product: Wazuh Wazuh. 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-2026-28221/ (Markdown: https://insights.sbomify.com/CVE-2026-28221/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-28221
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-28221
- OSV: https://osv.dev/vulnerability/CVE-2026-28221

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-28221/
Summaries are generated and may contain mistakes; the official description above is the record.