CVE-2026-17084

The stringprep module didnt 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.

Weakness

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.

Affected Software

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/105.html
• https://cwe.mitre.org/data/definitions/273.html
• https://cwe.mitre.org/data/definitions/34.html

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