CVE-2026-19553

HighCVSS 7.6

Published: 30/09/2026(UTC)Updated: 30/09/2026(UTC)Translated: 30/09/2026(UTC)NVD NIST

Summary

Risk Assessment

Applications may be exposed to man-in-the-middle attacks because certificate hostname verification is silently skipped. This could lead to interception of credentials or other sensitive information.

Recommendation

Pass a valid non-None and non-empty server_hostname value to SSLContext.wrap_bio(), asyncio.create_connection(), or asyncio.loop.start_tls(). Alternatively, upgrade to the latest Python version, which will raise a ValueError instead of silently skipping verification.

Other vulnerabilities in Python ssl module

CVE-2026-19445Critical
A remote, unauthenticated TLS client can crash a server or trigger a use-after-free if its sni_callback assigns a different context to SSLSocket.context (the documented way to select a certificate per server name) and nothing else keeps the original ssl.SSLContext alive. Typical cases are servers that create an SSLContext per connection or replace it while connections are open; servers that wrap their listening socket with it are not affected. Mitigation: keep a reference to every SSLContext that sets sni_callback for the lifetime of the server. TLS clients are not affected.

Original NVD description (English source)

ssl.SSLContext.wrap_bio() didn't require the server_hostname argument to not be None if ssl.SSLContext.check_hostname was set. Due to a missing parameter check in SSLObject, if the server_hostname argument isn't supplied then hostname verification would be silently skipped. This defect could lead to programs where certificate hostname verification *appeared* to be succeeding with SSLContext.check_hostname = True and no ValueError being raised due to misconfiguration. If the program passes a server_hostname value that isn't an empty string or None to any of these APIs then certificate hostname verification proceeds as expected and the program is not affected by this vulnerability. Mitigating this vulnerability doesn't require updating Python or applying the patch. To mitigate, pass a valid non-None and non-empty server_hostname value to SSLContext.wrap_bio(), asyncio.create_connection(), or asyncio.loop.start_tls() and certificate hostname verification will proceed as expected. Upgrading to the latest version of Python or applying the patch only changes the behavior from silently skipping hostname verification to raising a ValueError, similar to SSLContext.wrap_socket(), when server_hostname isn't supplied.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS