CVE-2025-15346: wolfSSL Python module vulnerable to Improper Authentication

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.3%, percentile 26: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 26% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes wolfssl (PyPI) < 5.8.4.post0, fixed in 5.8.4.post0. Check your lockfile, including transitive dependencies.

What it is

A vulnerability in the handling of verifymode = CERTREQUIRED in the wolfssl Python package (wolfssl-py) causes client certificate requirements to not be fully enforced. Because the WOLFSSLVERIFYFAILIFNOPEERCERT flag was not included, the behavior effectively matched CERTOPTIONAL: a peer certificate was verified if presented, but connections were incorrectly authenticated when no client certificate was provided. This results in improper authentication, allowing attackers to bypass mutual TLS (mTLS) client authentication by omitting a client certificate during the TLS handshake. The issue affects versions up to and including 5.8.2.

From the GitHub advisory

A vulnerability in the handling of verifymode = CERTREQUIRED in the wolfssl Python package (wolfssl-py) causes client certificate requirements to not be fully enforced.

Because the WOLFSSLVERIFYFAILIFNOPEERCERT flag was not included, the behavior effectively matched CERTOPTIONAL: a peer certificate was verified if presented, but connections were incorrectly authenticated when no client certificate was provided.

This results in improper authentication, allowing attackers to bypass mutual TLS (mTLS) client authentication by omitting a client certificate during the TLS handshake.

The issue affects versions up to and including 5.8.2.

Weakness type: CWE-306, CWE-287.

Product: wolfssl (PyPI) · Assigned by: wolfSSL · Published: 2026-01-07

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.33% probability of exploitation activity in the next 30 days; percentile 26.

Timeline

• 2026-01-07 — CVE record published by wolfSSL
• 2026-01-08 — CVE record last updated
• 2026-01-08 — GitHub-reviewed advisory GHSA-vj87-jj27-4h9c published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-vj87-jj27-4h9c github.com
2. CVE.org record CVE-2025-15346 cve.org
3. NVD entry CVE-2025-15346 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical PyPI advisories · Today’s Security Digest