Answer in brief
CVE-2026-44452 records a Medium severity (CVSS 5.9) vulnerability in h2o is vulnerable to heap overrun. The current sources do not mark it as known exploited. The current feed maps h2o/h2o (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 5.9. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps h2o/h2o (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| h2o/h2ogeneric | < 8dc37cb | Not reported |
Published upstream
Jul 16, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Jul 17, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Jul 17, 2026
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 8dc37cb, when h2o receives a ClientHello message over TLS or QUIC and it contains a zero-length SNI extension, the h2o server runs over the zero-length hostname while trying to copy the hostname, assuming that it is NULL-terminated. This is a potential denial-of-service attack vector in sense that it might trigger segmentation violation. This issue has been fixed by commit 8dc37cb.
Quoted source text, attributed separately from HOL analysis.
Answer in brief
CVE-2026-44452 records a Medium severity (CVSS 5.9) vulnerability in h2o is vulnerable to heap overrun. The current sources do not mark it as known exploited. The current feed maps h2o/h2o (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 5.9. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps h2o/h2o (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| h2o/h2ogeneric | < 8dc37cb | Not reported |
Published upstream
Jul 16, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Jul 17, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Jul 17, 2026
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 8dc37cb, when h2o receives a ClientHello message over TLS or QUIC and it contains a zero-length SNI extension, the h2o server runs over the zero-length hostname while trying to copy the hostname, assuming that it is NULL-terminated. This is a potential denial-of-service attack vector in sense that it might trigger segmentation violation. This issue has been fixed by commit 8dc37cb.
Quoted source text, attributed separately from HOL analysis.