What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 8.2 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2023-04-27 · updated 2026-06-17
• Weakness: CWE-824

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.

Affected products

• h2o: through 2.2.6; 2.3.0-beta1, 2.3.0-beta2

References

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

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