VulnerabilityModified

CVE-2026-23527

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.

CRITICAL 9.8EPSS 0.64%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (0.64%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.

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: 9.8 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS: 0.64% probability · 49th percentile
CISA KEV: Not listed
Weakness: CWE-444
Affected: h3/h3
Source: security-advisories@github.com

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.