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

Severity: medium (CVSS 5.9 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-20 · updated 2026-06-17
Weakness: CWE-208

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.

Affected products

h3js h3: 2.0.0, 2.0.1-rc1, 2.0.1-rc2, 2.0.1-rc3, 2.0.1-rc4, 2.0.1-rc5 (+3)

References

https://github.com/h3js/h3/pull/1283
https://github.com/h3js/h3/releases/tag/v2.0.1-rc.9
https://github.com/h3js/h3/security/advisories/GHSA-26f5-8h2x-34xh

Get alerted when CVE-2026-33129 or the next vulnerability affects your stack