CVE-2026-17084
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.
Does this matter?
Lower severity and a low EPSS score (0.60%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 4.0
- 6.0 MEDIUMCVSS:4.0/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/M
- EPSS
- 0.60% probability · 47th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-436
- Source
- cna@python.org
References
- https://github.com/python/cpython/commit/1e54caa096678a38afcabecabb1ff72400dd6bae
- https://github.com/python/cpython/commit/5181304bcec9cfc3c15311741c9154cdff2e3fd7
- 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/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
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.