# CVE-2025-6544: Deserialization Vulnerability in h2oai/h2o-3

> Attackers can execute arbitrary code and read system files via deserialization flaws in H2O-3 JDBC connection parameters.

- **Severity:** Critical 9.8 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 21 Sep 2025
- **Updated:** 22 Sep 2025
- **Also known as:** GHSA-5w3j-gwgh-4rfv, PYSEC-2026-349

## What is CVE-2025-6544?

CVE-2025-6544 is a critical unsafe deserialization vulnerability in h2oai/h2o-3, published on 21 Sep 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A deserialization vulnerability exists in h2oai/h2o-3 versions <= 3.46.0.8, allowing attackers to read arbitrary system files and execute arbitrary code. The vulnerability arises from improper handling of JDBC connection parameters, which can be exploited by bypassing regular expression checks and using double URL encoding. This issue impacts all users of the affected versions.

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2025-6544?

5 open source packages ship an affected version, including h2o and ai.h2o:h2o-core. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `h2o` | PyPI | All versions to 3.46.0.7 | None |
| `h2o` | PyPI | All versions to 3.46.0.7 | None |
| `h2o` | PyPI | All versions to 3.46.0.7 | None |
| `ai.h2o:h2o-core` | Maven | All versions to 3.46.0.7 | None |
| `ai.h2o:h2o-core` | Maven | All versions to 3.46.0.7 | None |

Products: H2o H2o.

## How do I fix CVE-2025-6544?

No fix has been published for CVE-2025-6544 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-6544 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-6544 exists.

## Other vulnerabilities in h2oai/h2o-3

- [CVE-2023-6016](https://insights.sbomify.com/CVE-2023-6016/): H2O Remote Code Execution via POJO Model Import (critical 10.0)
- [CVE-2024-10553](https://insights.sbomify.com/CVE-2024-10553/): Jdbc Deserialization in h2oai/h2o-3 (critical 9.8)
- [CVE-2023-6569](https://insights.sbomify.com/CVE-2023-6569/): External Control of File Name or Path in h2oai/h2o-3 (critical 9.3)
- [CVE-2023-6013](https://insights.sbomify.com/CVE-2023-6013/): H2O Local File Include (critical 9.3)
- [CVE-2023-6038](https://insights.sbomify.com/CVE-2023-6038/): Local File Inclusion in h2oai/h2o-3 (critical 9.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-6544 and fix it if it is affected.

What it is: CVE-2025-6544 is a critical unsafe deserialization vulnerability in h2oai/h2o-3, published on 21 Sep 2025. 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-2025-6544 exists.

Affected packages and fixed versions:
- h2o (PyPI): affected all versions up to 3.46.0.7; no fix listed
- h2o (PyPI): affected all versions up to 3.46.0.7; no fix listed
- h2o (PyPI): affected all versions up to 3.46.0.7; no fix listed
- ai.h2o:h2o-core (Maven): affected all versions up to 3.46.0.7; no fix listed
- ai.h2o:h2o-core (Maven): affected all versions up to 3.46.0.7; no fix listed

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-2025-6544/ (Markdown: https://insights.sbomify.com/CVE-2025-6544/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-6544
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-6544
- OSV: https://osv.dev/vulnerability/CVE-2025-6544

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-6544/
Summaries are generated and may contain mistakes; the official description above is the record.