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Vulnerability record · CVE-2026-23527 · published 15 January 2026

CVE-2026-23527: H3 http request smuggling vulnerability

HH3 · H3

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.

9.8 CVSS 3.1 Critical EPSS 0.64% · top 51.7% CWE-444 · HTTP request smuggling
9.8CVSS 3.1 base score
0.64%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
4References, 1 tagged exploit
17 Jun 2026Last modified by NVD

Description

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/h3js/h3/commit/618ccf4f37b8b6148bea7f36040471af45bfb097 Patch
https://github.com/h3js/h3/releases/tag/v1.15.5
https://github.com/h3js/h3/security/advisories/GHSA-mp2g-9vg9-f4cg ExploitVendor Advisory
https://simonkoeck.com/writeups/h3-transfer-encoding-request-smuggling

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Source: NIST National Vulnerability Database (record CVE-2026-23527), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.