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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33129?
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
Which versions are affected by CVE-2026-33129?
2 open source packages ship an affected version, including h3. It affects 1 product.
| Package | 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 include 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 h3 v1 has Request Smuggling (TE.TE) issue
- 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-2026-33490 h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on Unrelated Prefix-Matching Routes
Sources
Also known as GHSA-26f5-8h2x-34xh.