What is CVE-2021-3336?

CVE-2021-3336 is a high-severity vulnerability in Wolfssl, classified under Improper Certificate Validation. CVSS score: 8.1/10. Published 2021-01-29.

How severe is CVE-2021-3336?

High severity. CVSS v3 base score is 8.1 out of 10.

Is CVE-2021-3336 known to be exploited?

15 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Wolfssl

CVE-2021-3336

DoTls13CertificateVerify in tls13.c in wolfSSL before 4.7.0 does not cease processing for certain anomalous peer behavior (sending an ED22519, ED448, ECC, or RSA signature without the corresponding certificate). The client side is affected because man-in-the-middle attackers can impersonate TLS 1.3 servers.

Vulnerability class: Improper Certificate Validation

Published 2021-01-29 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.008 (54.6th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 55th percentile — 54.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000

Affected products

Wolfssl

Weakness classification (CWE)

CWE-295 — Improper Certificate Validation

Public proof-of-concept exploits

References

github.com/wolfSSL/wolfssl/pull/3676 (Patch, Third Party Advisory)
www.wolfssl.com/docs/security-vulnerabilities (Vendor Advisory)

Frequently asked questions

What is CVE-2021-3336?: CVE-2021-3336 is a high-severity vulnerability in Wolfssl, classified under Improper Certificate Validation. CVSS score: 8.1/10. Published 2021-01-29.
How severe is CVE-2021-3336?: High severity. CVSS v3 base score is 8.1 out of 10.
Is CVE-2021-3336 known to be exploited?: 15 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.