What is CVE-2026-33129?

CVE-2026-33129 is a medium-severity vulnerability in H3, classified under CWE-208. CVSS score: 5.9/10. Published 2026-03-20.

How severe is CVE-2026-33129?

Medium severity. CVSS v3 base score is 5.9 out of 10.

Vulnerability in H3

CVE-2026-33129

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.

Published 2026-03-20 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.004 (36.2th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 36.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.004 · change: +0.001

Affected products

H3 — versions 2.0.0, 2.0.1
H3js H3 — versions >= 2.0.1-beta.0, < 2.0.1-rc.9

Weakness classification (CWE)

CWE-208

References

github.com/h3js/h3/security/advisories/GHSA-26f5-8h2x-34xh (Exploit, Vendor Advisory)
github.com/h3js/h3/pull/1283 (Issue Tracking)
github.com/h3js/h3/releases/tag/v2.0.1-rc.9 (Patch)

Frequently asked questions

What is CVE-2026-33129?: CVE-2026-33129 is a medium-severity vulnerability in H3, classified under CWE-208. CVSS score: 5.9/10. Published 2026-03-20.
How severe is CVE-2026-33129?: Medium severity. CVSS v3 base score is 5.9 out of 10.