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CVE-2026-12003— CPython >3.11 Insecure Input Validation resulting in privilege escalation

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 Software Foundation CPython是Python Software Foundation基金会的编程语言解释器。 Python Software Foundation CPython 3.15.0之前版本存在权限许可和访问控制问题漏洞，该漏洞源于在Windows平台上VPATH变量设置为'..\\..'导致地标路径'..\\..\\Modules\\setup.local'位于安装目录之外，可能允许低权限用户创建地标及替代Lib文件夹，导致在限制性安装中发现该路径，造成权

CVSS 5.3 · Medium EPSS 0.15% · P3

Affected Version Matrix 5

VendorProduct Version RangeStatus
Python Software Foundation CPython < 3.11.16 affected
3.12.0< 3.12.14 affected
3.13.0< 3.13.15 affected
3.14.0< 3.14.7 affected
3.15.0a1< 3.15.0b3 affected
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I. Basic Information for CVE-2026-12003

Vulnerability Information
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Vulnerability Title
CPython >3.11 Insecure Input Validation resulting in privilege escalation
Source: CVE Program / CVE List V5
Vulnerability Description
To allow builds of Python to be run from an in-tree layout (rather than an installed file layout), the VPATH variable is defined at build time and used to locate certain landmarks - specifically, Modules/setup.local. When this landmark is found relative to VPATH relative to the executable, Python assumes it is running in a source tree and generates a different default sys.path. This code remains in release builds, so that release-ready builds can be built in-tree. On Windows, since builds are written to 'PCbuild/', the value of VPATH is set to '..\..', which results in a landmark of '..\..\Modules\setup.local'. This path is outside the install directory of Python, and may have different permissions, potentially allowing a low-privilege user to create the landmark and an alternative `Lib` folder that will be discovered by an otherwise restricted install. Such a setup occurs with the legacy default install location for all users (in the now superseded EXE installer), due to how Windows allows all users to create folders in the root directory of their OS drive. Our recommended mitigation on Windows is to migrate away from the legacy installer and use the new [Python install manager](https://www.python.org/downloads/latest/pymanager/) to install for the current user. Installs where the directory two levels above the Python installation directory have equivalent permissions are unaffected (in general, a per-user install cannot be modified at all by other users, removing any escalation of privilege risk, and could be directly modified by a privileged user, making the potential tampering irrelevant). Alternative mitigations might include preemptively creating and restricting access to a `Modules` directory. Be aware that only 3.13 and 3.14 will receive updated legacy installers - earlier fixes are only provided as sources. Platforms other than Windows allow VPATH to be overridden, but as they don't usually use a separated directory in the build for binaries, are unlikely to have a landmark reference outside of the install directory. The landmark detection involving VPATH is a fallback for when a more specific landmark - .\pybuilddir.txt - is absent, and was included for compatibility. Future releases of Python will no longer include the fallback, and so builds will need to generate or preserve the pybuilddir.txt file in order to work in-tree. This landmark file has been generated on Windows since 3.11, and on other platforms for longer.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
对搜索路径元素未加控制
Source: CVE Program / CVE List V5
Vulnerability Title
Python Software Foundation CPython 权限许可和访问控制问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Python Software Foundation CPython是Python Software Foundation基金会的编程语言解释器。 Python Software Foundation CPython 3.15.0之前版本存在权限许可和访问控制问题漏洞，该漏洞源于在Windows平台上VPATH变量设置为'..\\..'导致地标路径'..\\..\\Modules\\setup.local'位于安装目录之外，可能允许低权限用户创建地标及替代Lib文件夹，导致在限制性安装中发现该路径，造成权
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)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Python Software Foundation CPython 0 ~ 3.11.16 -

II. Public POCs for CVE-2026-12003

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III. Intelligence Information for CVE-2026-12003

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Patches & Fixes for CVE-2026-12003 (8)

Other References for CVE-2026-12003 (1)

IV. Related Vulnerabilities

Same product: CPython
Same vendor: Python Software Foundation
Same weakness: CWE-427

V. Comments for CVE-2026-12003

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