# 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.

- **Severity:** High 8.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Jan 2026
- **Updated:** 13 Apr 2026
- **Also known as:** GHSA-mp2g-9vg9-f4cg

## 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 (Inconsistent Interpretation of HTTP Requests)

## Which versions are affected by CVE-2026-23527?

2 open source packages ship an affected version, including h3. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `h3` | npm | All versions | 1.15.5 |
| `h3` | npm | All versions | 1.15.5 |

Products: 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](https://insights.sbomify.com/CVE-2026-33128/): h3 has a Server-Sent Events Injection via Unsanitized Newlines in Event Stream Fields (high 7.5)
- [CVE-2026-33131](https://insights.sbomify.com/CVE-2026-33131/): h3 has a middleware bypass with one gadget (high 7.4)
- [CVE-2026-33129](https://insights.sbomify.com/CVE-2026-33129/): h3 has an observable timing discrepancy in basic auth utils (medium 5.9)
- [CVE-2026-33490](https://insights.sbomify.com/CVE-2026-33490/): h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on Unrelated Prefix-Matching Routes (low 3.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23527 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-23527 in the wild and no public exploit code.

Affected packages and fixed versions:
- h3 (npm): affected all versions; fixed in 1.15.5
- h3 (npm): affected all versions; fixed in 1.15.5

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-23527/ (Markdown: https://insights.sbomify.com/CVE-2026-23527/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23527
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23527
- OSV: https://osv.dev/vulnerability/CVE-2026-23527

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23527/
Summaries are generated and may contain mistakes; the official description above is the record.