CVE-2026-23527: h3

Critical severity, CVSS 9.8. EPSS: 0.6% chance of exploitation in the next 30 days.

H3 is a minimal H(TTP) framework built for high performance and portability. Prior to 1.15.5, there is a critical HTTP Request Smuggling vulnerability. readRawBody is doing a strict case-sensitive check for the Transfer-Encoding header. It explicitly looks for "chunked", but per the RFC, this header should be case-insensitive. This vulnerability is fixed in 1.15.5.

Affected products

• h3 h3: before 1.15.5 (fixed in 1.15.5)

Published 2026-01-15. Last modified 2026-06-17.