Python Software Foundation up to 3.15.x SSLObject ssl.SSLContext.wrap_bio server_hostname input validation

Summaryinfo

A vulnerability classified as critical was found in Python Software Foundation Python up to 3.15.x. This affects the function ssl.SSLContext.wrap_bio of the component SSLObject. Such manipulation of the argument server_hostname leads to input validation. This vulnerability is traded as CVE-2026-19553. The attack may be launched remotely. There is no exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Python Software Foundation Python up to 3.15.x. It has been rated as critical. Affected by this issue is the function ssl.SSLContext.wrap_bio of the component SSLObject. The manipulation of the argument server_hostname with an unknown input leads to a input validation vulnerability. Using CWE to declare the problem leads to CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. Impacted is confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-19553 since 08/11/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available.

Upgrading to version 3.16.0 eliminates this vulnerability.

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Productinfo

Type

• Programming Language Software

Vendor

• Python Software Foundation

Name

• Python

Version

• 3.0
• 3.1
• 3.2
• 3.3
• 3.4
• 3.5
• 3.6
• 3.7
• 3.8
• 3.9
• 3.10
• 3.11
• 3.12
• 3.13
• 3.14
• 3.15

License

• open-source

CPE 2.3info

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CPE 2.2info

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