by Kastro
Paper/Archive/CVE-2026-23527

CVE-2026-23527

h3js h3 — h3 v1 has Request Smuggling (TE.TE) issue

EPSS 0.6%CVSS 9.8
critical.is priorityof 100
39
CVSS 9.8 (NVD)9.8 / 10 × 3029.4Not in CISA KEV+300.0EPSS percentile 50.0.500 × 2010.0No public exploit+100.0SSVC exploitation: none+100.0
Description · from the CVE record

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

ProductAffectedFixed inSource
h3< 1.15.5–CNA

Scores by source

NVD9.8CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
GitHub_M (CNA)8.9CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L
CISA ADPSSVCExploitation: none · Automatable: no · Technical impact: total

References

refgithub.com/h3js/h3/security/advisories/GHSA-mp2g-9vg9-f4cgrefgithub.com/h3js/h3/commit/618ccf4f37b8b6148bea7f36040471af45bfb097refgithub.com/h3js/h3/releases/tag/v1.15.5refsimonkoeck.com/writeups/h3-transfer-encoding-request-smuggling