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.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Python Software Foundation | CPython | unaffected |
|
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Solution
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Workaround
No workaround given by the vendor.
Wed, 30 Sep 2026 16:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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. | |
| Title | SSLContext.wrap_bio() missing validation of server_hostname parameter | |
| Weaknesses | CWE-297 | |
| References |
| |
| Metrics |
cvssV4_0
|
Projects
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MITRE
Status: PUBLISHED
Assigner: PSF
Published:
Updated: 2026-09-30T16:17:39.368Z
Reserved: 2026-08-11T15:22:03.833Z
Link: CVE-2026-19553
Vulnrichment
No data.
NVD
Status : Awaiting Analysis
Published: 2026-09-30T17:16:45.880
Modified: 2026-09-30T17:31:44.573
Link: CVE-2026-19553
Redhat
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OpenCVE Enrichment
Updated: 2026-09-30T17:30:19Z