PatchTheCVECVE-2023-41337: h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3
CVE-2023-41337 is a medium-severity flaw (CVSS 6.1) affecting h2o. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. In version 2.3.0-beta2 and prior, when h2o is configured to listen to multiple addresses or ports with each of them using different backend servers managed by multiple entities, a malicious backend entity that also has the opportunity to observe or inject packets exchanged between the client and h2o may misdirect HTTPS requests going to other backends and observe the contents of
Why this priority
- No elevated risk signals yet
A fixed release or distro patch exists.
Risk facts
| CVSS score | 6.1 (Medium) |
| Attack vector | Adjacent network |
| Attack complexity | High |
| Privileges needed | Low |
| User interaction | Required |
| EPSS exploit chance | 0.2% (top 92%) |
| CISA exploited list | No |
| Weakness | CWE-347 |
| Published | 2023-12-12 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2023-41337?
h2o: upgrade to newer than 2.2.6. Exact commands for each OS are on this page.
Is CVE-2023-41337 being exploited?
CVE-2023-41337 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2023-41337 affect?
CVE-2023-41337 affects h2o. Severity is medium (CVSS 6.1). h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. In version 2.3.0-beta2 and prior, when h2o is configured to listen to multiple addresses or ports with each of them using different backend servers managed by multiple enti
How urgent is CVE-2023-41337?
Priority 23/100. No elevated risk signals yet.
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