CVE-2026-19553
HIGHDescription
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.
How to fix
This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.
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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v4 Vector
Exploitability
Impact
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/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
Exploit Intelligence
Moderate risk: more likely to be exploited than 46% of all known CVEs.
References
Related Vulnerabilities
Other CWE-297 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2014-3522 | Medium | 4.0 | 5.6% | - | Fix |
| CVE-2018-10936 | High | 8.1 | 2.9% | - | Fix |
| CVE-2020-1887 | Critical | 9.1 | 1.6% | - | Fix |
| CVE-2024-2466 | Medium | 6.5 | 1.5% | - | Fix |
| CVE-2020-14387 | High | 7.4 | 1.1% | - | Fix |
| CVE-2020-15260 | Medium | 6.8 | 1.0% | - | Fix |
Common questions
How do I fix CVE-2026-19553?
Published advisories record a fix for 89 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2026-19553 being actively exploited?
Not that we know of. CVE-2026-19553 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.55% is the estimated probability that it will be exploited in the next 30 days. That is higher than 46% of all scored CVEs.
How severe is CVE-2026-19553?
CVE-2026-19553 has a CVSS v4 base score of 7.6, rated important. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2026-19553 affect?
Published advisories record a fix for pypy3 (Debian), python3.11 (Debian), python3.13 (Debian), python3.14 (Debian), and 85 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-10-16.