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Fencer Vulns
medium 5.3

CVE-2026-12003 json

CPython >3.11 Insecure Input Validation resulting in privilege escalation

published 2026-06-16 4 mo ago modified 2026-10-25 14 d ago also BIT-libpython-2026-12003 , BIT-python-2026-12003 , BIT-python-min-2026-12003 , EUVD-2026-37125

cvss
5.3
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 3%
public exploits
0
none known

Summary

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Such a setup occurs with the legacy default install location for all users (in the now superseded EXE installer), due to how Windows allows all users to create folders in the root directory of their OS drive.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.

Patch / fix

  • bitnami libpython 3.11.16, 3.12.14, 3.13.15, 3.14.7
  • bitnami python 3.11.16, 3.12.14, 3.13.15, 3.14.7
  • bitnami python-min 3.11.16, 3.12.14, 3.13.15, 3.14.7
  • Python Software Foundation CPython 3.11.16, 3.12.14, 3.13.15, 3.14.7, 3.15.0b3
  • python3.14 Debian 14 3.14.9-1

debian advisories DEBIAN-CVE-2026-12003

  • python3.13 hummingbird 1 3.13.15-1.3.hum1
  • python3.13-idle hummingbird 1 3.13.15-1.3.hum1
  • python3.13-libs hummingbird 1 3.13.15-1.3.hum1
  • python3.13-test hummingbird 1 3.13.15-1.3.hum1
  • python3.13-tkinter hummingbird 1 3.13.15-1.3.hum1
  • python3.13-freethreading hummingbird 1 3.13.15-1.3.hum1
  • python3.12 hummingbird 1 3.12.14-1.3.hum1
  • python3.12-idle hummingbird 1 3.12.14-1.3.hum1

red hat advisories RHSA-2026:68309RHSA-2026:68154RHSA-2026:68135RHSA-2026:67572

  • python3 Azure Linux 3.0 3.12.9-14

azure linux advisories AZL-90182

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-12003 updated cvss 7.8

python: Python: Privilege escalation due to insecure VPATH handling in Windows legacy installers

  • Red Hat Hardened Images python3.10
    affected: no fix planned “Will not fix”
  • Red Hat Hardened Images python3 3.14.7-1.2.hum1, python3.14 3.14.7-1.2.hum1, python3.11 3.11.16-1.4.hum1, python3.12 3.12.14-1.3.hum1, python3.13 3.13.15-1.3.hum1, python3-idle 3.14.7-1.2.hum1, +22 more
    fixed: vendor fix RHSA-2026:67572
  • Red Hat Enterprise Linux 6 python, tkinter, python-libs, python-test, python-tools Red Hat Enterprise Linux 7 python, python3, tkinter, python-libs, python-test, python-tools, +4 more Red Hat Enterprise Linux 8 scipy, python3, python36, python3.12, python-nose, python-wheel, +31 more Red Hat Enterprise Linux 9 python3, python3.9, python3.12, python3.14, python3-idle, python3-libs, +16 more Red Hat Enterprise Linux 10 python3.12, python3.14
    not affected: vulnerable code not present
  • Red Hat Hardened Images hi/python
    not affected: component not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
4 mo ago

Exploit prediction

0.14% chance of exploitation in the next 30 days, higher than 3% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 5.3 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
CNA 4.0 5.3 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected packages

ecosystem package affected fixed in
bitnami libpython
<3.11.16
>=3.12.0, <3.12.14
>=3.13.0, <3.13.15
>=3.14.0, <3.14.7
3.11.16
3.12.14
3.13.15
3.14.7
bitnami python
<3.11.16
>=3.12.0, <3.12.14
>=3.13.0, <3.13.15
>=3.14.0, <3.14.7
3.11.16
3.12.14
3.13.15
3.14.7
bitnami python-min
<3.11.16
>=3.12.0, <3.12.14
>=3.13.0, <3.13.15
>=3.14.0, <3.14.7
3.11.16
3.12.14
3.13.15
3.14.7

Affected products

  • Python Software Foundation CPython

Classification

Weakness
  • CWE-427 Uncontrolled Search Path Element

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.