CVE-2026-17084: Python Software Foundation Cpython

Medium severity, CVSS 6.0. EPSS: 0.7% chance of exploitation in the next 30 days.

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 Software Foundation Cpython: before 3.10.22 (fixed in 3.10.22); from 3.11.0, before 3.11.17 (fixed in 3.11.17); from 3.12.0, before 3.12.15 (fixed in 3.12.15); from 3.13.0, before 3.13.16 (fixed in 3.13.16); from 3.14.0, before 3.14.8 (fixed in 3.14.8); from 3.15.0a1, before 3.15.0rc2 (fixed in 3.15.0rc2)

Published 2026-08-18. Last modified 2026-10-02.