CVE-2026-19553
SSLContext.wrap_bio() missing validation of server_hostname parameter
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.
INFO
Published Date :
Sept. 30, 2026, 5:16 p.m.
Last Modified :
Oct. 16, 2026, 7:17 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
Affected Products
The following products are affected by CVE-2026-19553
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 4.0 | HIGH | 28c92f92-d60d-412d-b760-e73465c3df22 | ||||
| CVSS 4.0 | HIGH | [email protected] |
Solution
- Pass a non-None, non-empty server_hostname to wrap_bio().
- Pass a non-None, non-empty server_hostname to create_connection().
- Pass a non-None, non-empty server_hostname to start_tls().
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-19553.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-19553 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-19553
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-19553 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-19553 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Oct. 16, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-19553', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-10-16T18:33:08.291056Z'} -
CVE Modified by [email protected]
Oct. 03, 2026
Action Type Old Value New Value Added Affected Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19553.json">CVE-2026-19553</a> -
CVE Modified by [email protected]
Oct. 02, 2026
Action Type Old Value New Value Added Affected Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19553.json">CVE-2026-19553</a> -
CVE Modified by [email protected]
Oct. 01, 2026
Action Type Old Value New Value Added Reference https://github.com/python/cpython/commit/5867d4e4ae6d1062352baf6b497a4026e8578ccf Added Reference https://github.com/python/cpython/commit/bdebbf9b366ec91e9cd9daa0b3510c9e84b60b80 -
CVE Modified by [email protected]
Sep. 30, 2026
Action Type Old Value New Value Added Affected Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19553.json">CVE-2026-19553</a> Added Reference https://github.com/python/cpython/commit/869069d52ce0efab2f8c38197e92cdaaa312f1ed -
CVE Modified by [email protected]
Sep. 30, 2026
Action Type Old Value New Value Added Affected Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19553.json">CVE-2026-19553</a> Added Reference https://github.com/python/cpython/commit/1697ea386c707142555d98a1263176bbbc014a96 Added Reference https://github.com/python/cpython/commit/641390146a16a38e6701923f4ee4f1940ae77082 Added Reference https://github.com/python/cpython/commit/966bf426d0b6c31c1b0a255ff14a17143a466ced Added Reference https://github.com/python/cpython/commit/f4e43ba525187282f2011da0e6ffc0d2b08d8062 -
CVE Modified by af854a3a-2127-422b-91ae-364da2661108
Sep. 30, 2026
Action Type Old Value New Value Added Reference http://www.openwall.com/lists/oss-security/2026/09/30/16 -
New CVE Received by [email protected]
Sep. 30, 2026
Action Type Old Value New Value 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. Added CVSS V4.0 AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-297 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19553.json">CVE-2026-19553</a> Added Reference https://github.com/python/cpython/issues/156793 Added Reference https://github.com/python/cpython/pull/158503 Added Reference https://mail.python.org/archives/list/[email protected]/thread/QNZRG3YOAMTHDCMVCICXGY6YEFPY2VDL/