# CVE-2026-33129: h3 has an observable timing discrepancy in basic auth utils

> An attacker can deduce valid passwords character-by-character via timing side-channels in the basic auth utility, bypassing security protections.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Mar 2026
- **Updated:** 20 Mar 2026
- **Also known as:** GHSA-26f5-8h2x-34xh

## What is CVE-2026-33129?

CVE-2026-33129 is a medium-severity vulnerability in h3js h3, published on 20 Mar 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. Versions 2.0.1-beta.0 through 2.0.0-rc.8 contain a Timing Side-Channel vulnerability in the requireBasicAuth function due to the use of unsafe string comparison (!==). This allows an attacker to deduce the valid password character-by-character by measuring the server's response time, effectively bypassing password complexity protections. This issue is fixed in version 2.0.1-rc.9.

Weakness: CWE-208 (Observable Timing Discrepancy)

## Which versions are affected by CVE-2026-33129?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `h3` | npm | From 2.0.0-beta.0 | 2.0.1-rc.9 |
| `h3` | npm | From 2.0.0-beta.0 | 2.0.1-rc.9 |

Products: H3 H3.

## How do I fix CVE-2026-33129?

Upgrade h3 to 2.0.1-rc.9 or later.

## Is CVE-2026-33129 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33129 exists.

## Other vulnerabilities in h3js h3

- [CVE-2026-23527](https://insights.sbomify.com/CVE-2026-23527/): h3 v1 has Request Smuggling (TE.TE) issue (high 8.9)
- [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-2026-33490](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-2026-33129 and fix it if it is affected.

What it is: CVE-2026-33129 is a medium-severity vulnerability in h3js h3, published on 20 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33129 exists.

Affected packages and fixed versions:
- h3 (npm): affected from 2.0.0-beta.0; fixed in 2.0.1-rc.9
- h3 (npm): affected from 2.0.0-beta.0; fixed in 2.0.1-rc.9

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-2026-33129/ (Markdown: https://insights.sbomify.com/CVE-2026-33129/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33129
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33129
- OSV: https://osv.dev/vulnerability/CVE-2026-33129

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33129/
Summaries are generated and may contain mistakes; the official description above is the record.