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The vulnerability in the wolfSSL Python package (wolfssl-py) arises from incorrect handling of the verify_mode parameter when set to CERT_REQUIRED. In the underlying wolfSSL library, this mode should enforce mutual TLS (mTLS) by requiring a valid client certificate. However, the Python binding fails to include the WOLFSSL_VERIFY_FAIL_IF_NO_PEER_CERT flag during the SSL_CTX_set_verify call. This omission causes the behavior to default to CERT_OPTIONAL, where client certificates are verified only if presented. Consequently, during the TLS handshake, if a client connects without providing a certificate, the server incorrectly authenticates the connection. This flaw allows attackers to bypass mTLS client authentication entirely by omitting a client certificate. The issue stems from the mapping between Python’s ssl module constants and wolfSSL’s internal flags. Specifically, the wolfssl-py module does not translate CERT_REQUIRED to the necessary wolfSSL verification flags, leaving systems vulnerable. This improper authentication affects all versions up to and including 5.8.2, compromising security in environments relying on mTLS for access control. The vulnerability is critical as it undermines the fundamental trust model of mTLS, potentially granting unauthorized access to sensitive services.
Platform: wolfSSL Python module
Version: up to 5.8.2
Vulnerability: Improper Authentication
Severity: Critical
date: Jan 8 2026
Prediction: Patch expected soon
What Undercode Say:
Showing bash commands and codes related to the blog
pip list | grep wolfssl python -c "import wolfssl; print(wolfssl.<strong>version</strong>)"
import wolfssl ctx = wolfssl.SSLContext(wolfssl.PROTOCOL_TLS_SERVER) ctx.verify_mode = wolfssl.CERT_REQUIRED Vulnerable setting
How Exploit:
Attacker connects without client certificate to bypass mTLS authentication.
Protection from this CVE
Update wolfssl-py package.
Impact:
Unauthorized access bypass.
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Sources:
Reported By: github.com
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