Cyber Resilience

CVE-2026-33129

H3 2.0.0 … 2.0.1

Public PoC
Published
20 March 2026
Modified
20 March 2026
Patch / advisory
View advisory
CVSS Score v3.1 5.9
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS Score 0.0032 24th percentile
Risk Priority 35 floored blend · peak EPSS

Summary

CVE-2026-33129 is a medium-severity Observable Timing Discrepancy (CWE-208) vulnerability in H3 H3. Its CVSS base score is 5.9 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Password Guessing (T1110.001); ranked at the 24th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SI-2 (Flaw Remediation) and AC-7 (Unsuccessful Logon Attempts) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

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…

more

the server's response time, effectively bypassing password complexity protections. This issue is fixed in version 2.0.1-rc.9.

CWE(s)
CWE-208

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1110.001 Password Guessing Credential Access
Adversaries with no prior knowledge of legitimate credentials within the system or environment may guess passwords to attempt access to accounts.
attack.mitre.org →
Why these techniques?

Timing side-channel in basic auth enables efficient character-by-character password guessing.

Confidence: MEDIUM · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-23527Same product: H3 H3
CVE-2026-33128Same product: H3 H3
CVE-2026-33490Same product: H3 H3
CVE-2026-33131Same product: H3 H3
CVE-2026-6656Shared CWE-208
CVE-2026-56764Shared CWE-208
CVE-2026-47373Shared CWE-208
CVE-2025-70949Shared CWE-208
CVE-2026-47784Shared CWE-208
CVE-2026-43514Shared CWE-208

Affected Assets

h3
h3
2.0.0, 2.0.1

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • IA-5 Authenticator Management
  • AC-7 Unsuccessful Logon Attempts
Detect
Catch it (NIST detect / respond)
  • SI-2 Flaw Remediation
Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V11.2.4

Mitigating Controls (NIST 800-53 r5) AI

IA-5 Authenticator Management partial match
prevent

Requires secure authenticator verification methods that eliminate observable timing differences during password comparison in requireBasicAuth.

AC-7 Unsuccessful Logon Attempts partial match
prevent

Limits the number of authentication attempts, reducing an attacker's ability to perform repeated timing measurements needed to extract the password character-by-character.

SI-2 Flaw Remediation good match
respond

Mandates prompt application of the vendor patch that replaces the unsafe != comparison with a constant-time equivalent.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require constant-time implementations that eliminate observable timing discrepancies.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.17 Clock synchronization none match
none

Consistent reference clocks limit the attacker's ability to measure or manipulate timing differences that could reveal internal state or processing paths.

References