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CVE-2026-3446— Base64 decoding stops at first padded quad by default

Quick assessment

Affected
Python Software Foundation CPython
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Python是Python基金会的一套开源的、面向对象的程序设计语言。该语言具有可扩展、支持模块和包、支持多种平台等特点。 Python存在安全漏洞，该漏洞源于base64.b64decode及相关函数在遇到第一个填充四元组后即停止解码，可能导致数据被接受并被其他实现以不同方式处理。

AI Predicted 5.3 Difficulty: Moderate EPSS 0.22% · P12

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-3446

Vulnerability Information
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Vulnerability Title
Base64 decoding stops at first padded quad by default
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Python 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Python是Python基金会的一套开源的、面向对象的程序设计语言。该语言具有可扩展、支持模块和包、支持多种平台等特点。 Python存在安全漏洞，该漏洞源于base64.b64decode及相关函数在遇到第一个填充四元组后即停止解码，可能导致数据被接受并被其他实现以不同方式处理。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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Affected Products

Vendor Product Affected Versions CPE Subscribe
Python Software Foundation CPython 0 ~ 3.13.13 -

II. Public POCs for CVE-2026-3446

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III. Intelligence Information for CVE-2026-3446

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Patches & Fixes for CVE-2026-3446 (4)

Mailing List Discussions for CVE-2026-3446 (1)

IV. Related Vulnerabilities

Same product: CPython
Same vendor: Python Software Foundation

V. Comments for CVE-2026-3446

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