CVE-2026-19553

Summary

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.

Affected Software

VendorProductVersion RangeStatus
Python Software FoundationCPython0 < 3.12.15affected
Python Software FoundationCPython3.13.0 < 3.13.16affected
Python Software FoundationCPython3.14.0 < 3.14.8affected
Python Software FoundationCPython3.15.0a1 < 3.15.0affected

Weaknesses

  • CWE-297: CWE-297

ADP Enrichment

CVE Program Container

Additional References

References