CVE-2026-23527
HIGHh3 < 1.15.5 - HTTP Request Smuggling via Transfer-Encoding Header Case Mismatch
Title source: llmDescription
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.
References (4)
Core 4
Core References
Exploit, Vendor Advisory x_refsource_confirm
https://github.com/h3js/h3/security/advisories/GHSA-mp2g-9vg9-f4cg
Patch x_refsource_misc
https://github.com/h3js/h3/commit/618ccf4f37b8b6148bea7f36040471af45bfb097
X_Refsource_Misc x_refsource_misc
https://github.com/h3js/h3/releases/tag/v1.15.5
X_Refsource_Misc x_refsource_misc
https://simonkoeck.com/writeups/h3-transfer-encoding-request-smuggling
Scores
CVSS v3
8.9
EPSS
0.0058
EPSS Percentile
42.7%
Attack Vector
NETWORK
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L
CISA SSVC
Vulnrichment
Exploitation
none
Automatable
no
Technical Impact
total
Details
CWE
CWE-444
Status
published
Products (3)
h3/h3
< 1.15.5
h3js/h3
< 1.15.5
npm/h3
0 - 1.15.5npm
Published
Jan 15, 2026
Tracked Since
Feb 18, 2026