CVE-2026-3446

MEDIUM

Base64 decoding stops at first padded quad by default

Title source: cna

Description

When calling base64.b64decode() or related functions the decoding process would stop after encountering the first padded quad regardless of whether there was more information to be processed. This can lead to data being accepted which may be processed differently by other implementations. Use "validate=True" to enable stricter processing of base64 data.

References (6)

[Patch] https://github.com/python/cpython/pull/145267

[Issue Tracking] https://github.com/python/cpython/issues/145264

[Vendor Advisory] https://mail.python.org/archives/list/[email protected]/thread/F5ZT5ICGJ6CKXVUJ34YBVY7WOZ5SHG53/

[Patch] https://github.com/python/cpython/commit/1f9958f909c1b41a4ffc0b613ef8ec8fa5e7c474

[Patch] https://github.com/python/cpython/commit/4561f6418a691b3e89aef0901f53fe0dfb7f7c0e

[Patch] https://github.com/python/cpython/commit/e31c55121620189a0d1a07b689762d8ca9c1b7fa

View Patch ZIP pw:eip

Scores

CVSS v4 6.0

EPSS 0.0003

EPSS Percentile 7.0%

CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Details

CWE

CWE-345

Status published

Products (3)

Python Software Foundation/CPython < 3.13.13

Python Software Foundation/CPython 3.14.0 - 3.14.4

Python Software Foundation/CPython 3.15.0a1 - 3.15.0a8

Published Apr 10, 2026

Tracked Since Apr 11, 2026