CVE-2026-23527 h3 v1 has Request Smuggling (TE.TE) issue
An attacker can exploit case-sensitive header checks to perform HTTP request smuggling, potentially bypassing security controls or accessing unauthorized data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-23527?
CVE-2026-23527 is a high-severity vulnerability in h3js h3, published on 15 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-444
Which versions are affected by CVE-2026-23527?
2 open source packages ship an affected version, including h3. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
h3 npm | All versions | 1.15.5 |
h3 npm | All versions | 1.15.5 |
Products include H3 H3.
How do I fix CVE-2026-23527?
Upgrade h3 to 1.15.5 or later.
Is CVE-2026-23527 being exploited?
There is no known exploitation of CVE-2026-23527 in the wild and no public exploit code.
Other vulnerabilities in h3js h3
- CVE-2026-33128 h3 has a Server-Sent Events Injection via Unsanitized Newlines in Event Stream Fields
- CVE-2026-33131 h3 has a middleware bypass with one gadget
- CVE-2026-33129 h3 has an observable timing discrepancy in basic auth utils
- CVE-2026-33490 h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on Unrelated Prefix-Matching Routes
Sources
Also known as GHSA-mp2g-9vg9-f4cg.