CVE-2026-19553highCWE-297

SSLContext.wrap_bio() missing validation of server_hostname parameter

41Vexday Risk Score

No sign of exploitation. It has a public proof of concept.

ssvc Attendcvss 7.6epss 0.4%

from disclosure to weapon2 days

Published on NVDSep 30

1st PoC+2d

exploitation probability

0.4%top 68% of all CVEs

observed exploitation

nono source reports it

1 public exploit(s)

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.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Affected products

Python Software Foundation · CPython

public PoCs found — 1

githubgithub.com/abraxas/cve-2026-19553-wrap-bio★ 0

⚠ Public resources, to assess the exposure of systems you control or are authorized to test. Test only with authorization.

References