HighCVE-2026-19553

SSLContext.wrap_bio() missing validation of server_hostname parameter (CVE-2026-19553)

Published 30.09.2026Last modified 16.10.2026Sources: Red Hat, BSI, Msrc Update Guide, OSV, CVE.org, SUSE, Debian LTS

Public exploit

What is affected, what to do

An exploit is publicly available. Update Python Software Foundation CPython to version 3.10.22, Python Software Foundation CPython to version 3.11.17, Python Software Foundation CPython to version 3.12.15.

Affected: Python Software Foundation CPython lt *..3.10.22
Python Software Foundation CPython lt 3.11.0..3.11.17
Python Software Foundation CPython lt 3.12.0..3.12.15
Python Software Foundation CPython lt 3.13.0..3.13.16
Python Software Foundation CPython lt 3.14.0..3.14.8
Python Software Foundation CPython lt 3.15.0a1..3.15.0rc3
Fixed in: Python Software Foundation CPython 3.10.22
Python Software Foundation CPython 3.11.17
Python Software Foundation CPython 3.12.15
Python Software Foundation CPython 3.13.16
Python Software Foundation CPython 3.14.8
Python Software Foundation CPython 3.15.0rc3

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Metrics

7.6

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: Vendor (CNA), CVSS v4

7.6

CVSS v4

Severity High on the scale from 0 to 10.

Source: Red Hat, BSI, Msrc Update Guide, OSV, CVE.org, SUSE, Debian LTS

0.5 %

EPSS score

Low — model estimates < 1% exploitation likelihood.

Source: FIRST EPSS, percentile 45.6

Show all metrics

Severity: High
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 84.65 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: PoC (publicly reported)
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 7.6 Methodology
CVSS v4 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 7.6
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 0.5 %; Low — model estimates < 1% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 45.6; High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: —
Published: 30.09.2026
CWE CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect. Read in glossary: CWE-297

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

A flaw was found in Python. When establishing secure connections using the SSLContext.wrap_bio() function with hostname checking enabled, the module fails to validate that a target server hostname is supplied. Because of this missing check, certificate hostname verification is silently skipped rather than triggering an error. A remote man-in-the-middle attacker could exploit this defect to spoof trusted endpoints and intercept or tamper with sensitive encrypted traffic.

Source: redhat_csaf, BSI WID Portal, BSI CSAF, Microsoft Security Update Guide, OSV (Open Source Vulnerabilities), cvelistv5, NVD (NIST), suse_csaf, Debian LTS Advisories

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
Python Software Foundation	CPython	`3.15.0a1 – < 3.15.0rc3` `3.13.0 – < 3.13.16` `3.14.0 – < 3.14.8` `3.12.0 – < 3.12.15` `3.11.0 – < 3.11.17` `< 3.10.22`	`3.15.0rc3` `3.13.16` `3.14.8` `3.12.15` `3.11.17` `3.10.22`
Open Source	Python	`CPython`	—

Distribution and container packages (4)

Downstream packages (e.g. Bitnami, Debian, Ubuntu, Red Hat). Versions refer to the distribution, not the vendor.

Distribution and container packages
		Affected versions	Fixed in
bitnami	python-min	`3.13.0` `3.12.0` `3.14.0` `3.11.0`	— — — —

Vendors and products

Affected operating systems

Affected operating systems

Linux	debian	python3.11	`bookworm`

Weakness classes (CWE)

CWE-297Improper Validation of Certificate with Host Mismatch
Variant
The product communicates with a host that provides a certificate, but the product does not properly ensure that the certificate is actually associated with that host.
Entry at MITRE CWE-297

Public exploit references

Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

Public exploit references

PoC-in-GitHub (nomi-sec)	cve-2026-19553-wrap-bio (opens in a new tab)github.com	PoC (publicly reported)reported, not verified	02.10.2026

References & sources

github.compython/cpython/pull/158503Patch
github.compython/cpython/issues/156793Issue tracking
mail.python.orgarchives/list/security-announce@python.org/thread/QNZRG3YOAMTHD…Vendor advisory
openwall.comlists/oss-security/2026/09/30/16
github.compython/cpython/commit/1697ea386c707142555d98a1263176bbbc014a96Patch
github.compython/cpython/commit/641390146a16a38e6701923f4ee4f1940ae77082Patch
github.compython/cpython/commit/966bf426d0b6c31c1b0a255ff14a17143a466cedPatch
github.compython/cpython/commit/f4e43ba525187282f2011da0e6ffc0d2b08d8062Patch
github.compython/cpython/commit/869069d52ce0efab2f8c38197e92cdaaa312f1edPatch
github.compython/cpython/commit/5867d4e4ae6d1062352baf6b497a4026e8578ccffix, Patch
github.compython/cpython/commit/bdebbf9b366ec91e9cd9daa0b3510c9e84b60b80fix, Patch
NVD (NIST)vuln/detail/CVE-2026-19553web

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

16.10.2026Record modifiedCISA ADP

CISA assessment (SSVC): exploitation: none known, automatable: no

Show the original change

Individual changes of this event as published by NVD
Type	Action	Before	After
SSVC assessment	added	—	{"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"}

Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

03.10.2026Record modifiedpython.org

1 individual change: Affected versions (publisher)

Show the original change

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19553.json">CVE-2026-19553</a>

Source identifier: cna@python.org

02.10.2026Record modifiedpython.org

1 individual change: Affected versions (publisher)

Show the original change

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19553.json">CVE-2026-19553</a>

Source identifier: cna@python.org

01.10.2026Record modifiedpython.org

New references:

Show 2 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://github.com/python/cpython/commit/5867d4e4ae6d1062352baf6b497a4026e8578ccf
Reference	added	—	https://github.com/python/cpython/commit/bdebbf9b366ec91e9cd9daa0b3510c9e84b60b80

Source identifier: cna@python.org

30.09.2026Record modifiedpython.org

New references:

https://github.com/python/cpython/commit/869069d52ce0efab2f8c38197e92cdaaa312f1ed

Show 2 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19553.json">CVE-2026-19553</a>
Reference	added	—	https://github.com/python/cpython/commit/869069d52ce0efab2f8c38197e92cdaaa312f1ed

Source identifier: cna@python.org

Show 3 older changes

30.09.2026Record modifiedpython.org

New references:

Show 5 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19553.json">CVE-2026-19553</a>
Reference	added	—	https://github.com/python/cpython/commit/1697ea386c707142555d98a1263176bbbc014a96
Reference	added	—	https://github.com/python/cpython/commit/641390146a16a38e6701923f4ee4f1940ae77082
Reference	added	—	https://github.com/python/cpython/commit/966bf426d0b6c31c1b0a255ff14a17143a466ced
Reference	added	—	https://github.com/python/cpython/commit/f4e43ba525187282f2011da0e6ffc0d2b08d8062

Source identifier: cna@python.org

30.09.2026Record modifiedCVE Program
New references:
- http://www.openwall.com/lists/oss-security/2026/09/30/16
Show the original change
Individual changes of this event as published by NVD
Type Action Before After
Reference added
—
http://www.openwall.com/lists/oss-security/2026/09/30/16
Source identifier: af854a3a-2127-422b-91ae-364da2661108

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	http://www.openwall.com/lists/oss-security/2026/09/30/16

30.09.2026Receivedpython.org

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

Weakness type: CWE-297

Description added or changed

New references:

Show 7 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Description	added	—	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	added	—	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
Weakness type (CWE)	added	—	CWE-297
Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19553.json">CVE-2026-19553</a>
Reference	added	—	https://github.com/python/cpython/issues/156793
Reference	added	—	https://github.com/python/cpython/pull/158503
Reference	added	—	https://mail.python.org/archives/list/security-announce@python.org/thread/QNZRG3YOAMTHDCMVCICXGY6YEFPY2VDL/

Source identifier: cna@python.org

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