CVE-2026-19553SSLContext.wrap_bio() missing validation of server_hostname parameter
Updated under an hour ago ()
Does this affect you?
It affects Python Software Foundation CPython. Add what you run to find out whether that includes you.
EPSS puts the chance of exploitation in the next 30 days at 0.40%, higher than 32% of scored CVEs.
Do this next
Free account, 1 product
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
- 7.6 HIGH (v4.0, CNA)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
- Weakness (CWE)
- CWE-297
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- 0.40% (percentile 32)
- Assigned by
- PSF
- NVD analysis
- Awaiting Analysis
- Record last updated
- Oct 16, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Python Software Foundation CPython python_software_foundation:cpython (from the name) | before 3.10.22; from 3.11.0 before 3.11.17; from 3.12.0 before 3.12.15; from 3.13.0 before 3.13.16; from 3.14.0 before 3.14.8; from 3.15.0a1 before 3.15.0rc3 | CNA record |
References
- https://github.com/python/cpython/pull/158503patch
- https://github.com/python/cpython/issues/156793issue-tracking
- https://mail.python.org/archives/list/security-announce@python.org/thread/QNZRG3YOAMTHDCMVCICXGY6YEFPY2VDL/vendor-advisory
- https://github.com/python/cpython/commit/1697ea386c707142555d98a1263176bbbc014a96patch
- https://github.com/python/cpython/commit/641390146a16a38e6701923f4ee4f1940ae77082patch
- https://github.com/python/cpython/commit/966bf426d0b6c31c1b0a255ff14a17143a466cedpatch
- https://github.com/python/cpython/commit/f4e43ba525187282f2011da0e6ffc0d2b08d8062patch
- https://github.com/python/cpython/commit/869069d52ce0efab2f8c38197e92cdaaa312f1edpatch
- https://github.com/python/cpython/commit/5867d4e4ae6d1062352baf6b497a4026e8578ccfpatch
- https://github.com/python/cpython/commit/bdebbf9b366ec91e9cd9daa0b3510c9e84b60b80patch
- http://www.openwall.com/lists/oss-security/2026/09/30/16
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.