What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 6.0 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-18 · updated 2026-10-22
• Weakness: CWE-436

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.

Affected products

• Python: 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 3.15.0rc2 — fixed in 3.10.22, 3.11.17, 3.12.15, 3.13.16, 3.14.8, 3.15.0rc2

How to fix

Upgrade to a fixed version: Python 3.10.22, 3.11.17, 3.12.15, 3.13.16. Check the vendor advisory for mitigations.

References

• https://github.com/python/cpython/commit/1e54caa096678a38afcabecabb1ff72400dd6bae
• https://github.com/python/cpython/commit/5181304bcec9cfc3c15311741c9154cdff2e3fd7
• https://github.com/python/cpython/commit/69f92ebaec681e9149dfd70fd02d4ed52d2a6296
• https://github.com/python/cpython/commit/7e109d084d55e7eb25837a5f3b47ef9beee547bc
• https://github.com/python/cpython/commit/c016c2535b74227fddf2cf7334dbfead6c930214
• https://github.com/python/cpython/commit/c28b121a4f0b975937c8b5a1b4934bb361d84296
• https://github.com/python/cpython/commit/c42790b34f634051750e5da340d17c7da19e4784
• https://github.com/python/cpython/commit/d397a4979cfc80a8cd6c73838aa10e9c8cf5ef72
• https://github.com/python/cpython/issues/155292
• https://github.com/python/cpython/pull/155293
• https://mail.python.org/archives/list/security-announce@python.org/thread/EUHHTC6EV7HCLSUHP25C5VHSV4V2MUZN/
• http://www.openwall.com/lists/oss-security/2026/08/18/2

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