MediumCVE-2026-17084

stringprep.map_table_b2() deviates from RFC 3454 Table B.2 (CVE-2026-17084)

Published 18.08.2026Last modified 22.10.2026Sources: SUSE, BSI, CVE.org, Msrc Update Guide, Red Hat, OSV, Debian LTS

What is affected, what to do

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..3.15.0rc2
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 3.15.0rc2

Not sure whether and how you are affected? Ask a question about this vulnerability

Metrics

6.0

Priority

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

Source: Vendor (CNA), CVSS v4

6.0

CVSS v4

Severity Medium on the scale from 0 to 10.

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

0.7 %

EPSS score

Low — model estimates < 1% exploitation likelihood.

Source: FIRST EPSS, percentile 54.2

Show all metrics

Severity: Medium
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: 77.25 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: no public PoC known
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: 6.0 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: 6.0
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: 0.7 %; 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: 54.2; 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: 18.08.2026
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-436

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: Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
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

The "stringprep" module didn't process characters from RFC 3454 tables B.2 or B.3 correctly: the latest Unicode codepoint attributes were used instead of the specified Unicode 3.2.0. This behavior would cause mismatches when processing domain names using IDNA 2003 (the "idna" codec) and the in_table_b2() function of the "stringprep" module. This only affects domain names containing characters that were not previously registered or had their Unicode attributes such as case-folding behavior updated since Unicode 3.2.0.

Source: suse_csaf, BSI WID Portal, BSI CSAF, NVD (NIST), Microsoft Security Update Guide, cvelistv5, redhat_csaf, OSV (Open Source Vulnerabilities), 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 – < 3.15.0rc2` `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`	`3.15.0rc2` `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-436Interpretation Conflict
Class
Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.
Entry at MITRE CWE-436

References & sources

github.compython/cpython/pull/155293Patch
github.compython/cpython/issues/155292Issue tracking
mail.python.orgarchives/list/security-announce@python.org/thread/EUHHTC6EV7HCL…Vendor advisory
openwall.comlists/oss-security/2026/08/18/2
github.compython/cpython/commit/7e109d084d55e7eb25837a5f3b47ef9beee547bcPatch
github.compython/cpython/commit/5181304bcec9cfc3c15311741c9154cdff2e3fd7Patch
NVD (NIST)vuln/detail/CVE-2026-17084web
github.compython/cpython/commit/1e54caa096678a38afcabecabb1ff72400dd6baeweb, Patch
github.compython/cpython/commit/c016c2535b74227fddf2cf7334dbfead6c930214web, Patch
github.compython/cpython/commit/c28b121a4f0b975937c8b5a1b4934bb361d84296web, Patch
github.compython/cpython/commit/c42790b34f634051750e5da340d17c7da19e4784web, Patch
github.compython/cpython/commit/69f92ebaec681e9149dfd70fd02d4ed52d2a6296fix, Patch
github.compython/cpython/commit/d397a4979cfc80a8cd6c73838aa10e9c8cf5ef72fix, Patch

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).

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/2026/17xxx/CVE-2026-17084.json">CVE-2026-17084</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/69f92ebaec681e9149dfd70fd02d4ed52d2a6296
Reference	added	—	https://github.com/python/cpython/commit/d397a4979cfc80a8cd6c73838aa10e9c8cf5ef72

Source identifier: cna@python.org

30.09.2026Record 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/2026/17xxx/CVE-2026-17084.json">CVE-2026-17084</a>

Source identifier: cna@python.org

10.09.2026Record 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/c28b121a4f0b975937c8b5a1b4934bb361d84296
Reference	added	—	https://github.com/python/cpython/commit/c42790b34f634051750e5da340d17c7da19e4784

Source identifier: cna@python.org

09.09.2026Record modifiedpython.org
New references:
- https://github.com/python/cpython/commit/c016c2535b74227fddf2cf7334dbfead6c930214
Show the original change
Individual changes of this event as published by NVD
Type Action Before After
Reference added
—
https://github.com/python/cpython/commit/c016c2535b74227fddf2cf7334dbfead6c930214
Source identifier: cna@python.org

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://github.com/python/cpython/commit/c016c2535b74227fddf2cf7334dbfead6c930214

Show 5 older changes

05.09.2026Record modifiedpython.org
New references:
- https://github.com/python/cpython/commit/1e54caa096678a38afcabecabb1ff72400dd6bae
Show the original change
Individual changes of this event as published by NVD
Type Action Before After
Reference added
—
https://github.com/python/cpython/commit/1e54caa096678a38afcabecabb1ff72400dd6bae
Source identifier: cna@python.org

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://github.com/python/cpython/commit/1e54caa096678a38afcabecabb1ff72400dd6bae

02.09.2026Record modifiedpython.org

New references:

and 1 more reference

Show 11 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/2026/17xxx/CVE-2026-17084.json">CVE-2026-17084</a>
Reference	added	—	https://github.com/python/cpython/commit/5181304bcec9cfc3c15311741c9154cdff2e3fd7
Reference	added	—	https://github.com/python/cpython/commit/7e109d084d55e7eb25837a5f3b47ef9beee547bc
Reference	added	—	https://github.com/python/cpython/issues/155292
Reference	added	—	https://github.com/python/cpython/pull/155293
Reference	added	—	https://mail.python.org/archives/list/security-announce@python.org/thread/EUHHTC6EV7HCLSUHP25C5VHSV4V2MUZN/
Reference	removed	https://github.com/python/cpython/commit/5181304bcec9cfc3c15311741c9154cdff2e3fd7	—
Reference	removed	https://github.com/python/cpython/commit/7e109d084d55e7eb25837a5f3b47ef9beee547bc	—
Reference	removed	https://github.com/python/cpython/issues/155292	—
Reference	removed	https://github.com/python/cpython/pull/155293	—
Reference	removed	https://mail.python.org/archives/list/security-announce@python.org/thread/EUHHTC6EV7HCLSUHP25C5VHSV4V2MUZN/	—

Source identifier: cna@python.org

02.09.2026Record modifiedCVE Program

New references:

http://www.openwall.com/lists/oss-security/2026/08/18/2

Show 2 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	http://www.openwall.com/lists/oss-security/2026/08/18/2
Reference	removed	http://www.openwall.com/lists/oss-security/2026/08/18/2	—

Source identifier: af854a3a-2127-422b-91ae-364da2661108

19.08.2026Record modifiedpython.org
New references:
- https://github.com/python/cpython/commit/5181304bcec9cfc3c15311741c9154cdff2e3fd7
Show the original change
Individual changes of this event as published by NVD
Type Action Before After
Reference added
—
https://github.com/python/cpython/commit/5181304bcec9cfc3c15311741c9154cdff2e3fd7
Source identifier: cna@python.org

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://github.com/python/cpython/commit/5181304bcec9cfc3c15311741c9154cdff2e3fd7

18.08.2026Receivedpython.org

CVSS V4.0: AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Description added or changed

New references:

Show 6 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	CPython
Description	added	—	The "stringprep" module didn't process characters from RFC 3454 tables B.2 or B.3 correctly: the latest Unicode codepoint attributes were used instead of the specified Unicode 3.2.0. This behavior would cause mismatches when processing domain names using IDNA 2003 (the "idna" codec) and the in_table_b2() function of the "stringprep" module. This only affects domain names containing characters that were not previously registered or had their Unicode attributes such as case-folding behavior updated since Unicode 3.2.0.
CVSS	added	—	AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/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
Reference	added	—	https://github.com/python/cpython/issues/155292
Reference	added	—	https://github.com/python/cpython/pull/155293
Reference	added	—	https://mail.python.org/archives/list/security-announce@python.org/thread/EUHHTC6EV7HCLSUHP25C5VHSV4V2MUZN/

Source identifier: cna@python.org

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<a href="https://intel.neosec.eu/en/cve/CVE-2026-17084"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-17084.svg?lang=en" alt="CVE-2026-17084 – NEOSEC Intel" height="20"></a>