# CVE-2023-30847: H2O vulnerable to read from uninitialized pointer in the reverse proxy handler

> An attacker can cause crashes or leak sensitive information to backend servers by sending invalid HTTP requests to the H2O reverse proxy handler.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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:** 27 Apr 2023
- **Updated:** 30 Jan 2025
- **Also known as:** GHSA-p5hj-phwj-hrvx, UBUNTU-CVE-2023-30847

## What is CVE-2023-30847?

CVE-2023-30847 is a high-severity vulnerability in h2o, published on 27 Apr 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

H2O is an HTTP server. In versions 2.3.0-beta2 and prior, when the reverse proxy handler tries to processes a certain type of invalid HTTP request, it tries to build an upstream URL by reading from uninitialized pointer. This behavior can lead to crashes or leak of information to back end HTTP servers. Pull request  number 3229 fixes the issue. The pull request has been merged to the `master` branch in commit f010336. Users should upgrade to commit f010336 or later.

Weakness: CWE-824 (Access of Uninitialized Pointer)

## Which versions are affected by CVE-2023-30847?

It affects 1 product.


Products: Dena H2o.

## How do I fix CVE-2023-30847?

No fix has been published for CVE-2023-30847 yet. Limit exposure of the affected software until one is available.

## Is CVE-2023-30847 being exploited?

There is no known exploitation of CVE-2023-30847 in the wild and no public exploit code.

## Other vulnerabilities in h2o

- [CVE-2018-0608](https://insights.sbomify.com/CVE-2018-0608/): Memory corruption in H2O (critical 9.8)
- [CVE-2016-7835](https://insights.sbomify.com/CVE-2016-7835/): Use after free in H2O (critical 9.1)
- [CVE-2017-10868](https://insights.sbomify.com/CVE-2017-10868/): Denial of service in H2O (high 7.5)
- [CVE-2017-10869](https://insights.sbomify.com/CVE-2017-10869/): Memory corruption in H2O (high 7.5)
- [CVE-2017-10908](https://insights.sbomify.com/CVE-2017-10908/): Denial of service in H2O (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-30847 and fix it if it is affected.

What it is: CVE-2023-30847 is a high-severity vulnerability in h2o, published on 27 Apr 2023. 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-2023-30847 in the wild and no public exploit code.

Affected product: h2o. 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-2023-30847/ (Markdown: https://insights.sbomify.com/CVE-2023-30847/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-30847
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-30847
- OSV: https://osv.dev/vulnerability/CVE-2023-30847

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-30847/
Summaries are generated and may contain mistakes; the official description above is the record.