CVE-2026-23527: h3 v1 has Request Smuggling (TE.TE) issue

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-01-15 · updated 2026-06-17
Weakness: CWE-444

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.

Affected products

h3js h3: before 1.15.5 — fixed in 1.15.5

How to fix

Upgrade to a fixed version: h3js h3 1.15.5. Check the vendor advisory for mitigations.

References

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

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