Skip to main content
CVE-2026-12003VulnerabilityPublished Updated

Cython: To allow builds of Python to be run from an in-tree layout (rather than an installed file layout), the VPATH

Affects cythonSource GCVE Database

0
Compare
Authoritative record:CVE-2026-12003· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium.

Data as of 9 Nov 2026, 14:21 UTC

CVSS 4.0 base score
5.3Medium
How severe the flaw is on the 0–10 CVSS scale.
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

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 16 Jun 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 9 Nov 2026.

What to do

Affected software

ProductAffectedFixed in
Ubuntu 26.10cythonpkg:deb/ubuntu/cython?arch=source&distro=stonkingOther threatsAffected
  • =3.1.6+dfsg-1ubuntu2
Fixed in–
Ubuntu 25.10cythonpkg:deb/ubuntu/cython?arch=source&distro=questingOther threatsAffected
  • =3.0.11+dfsg-2ubuntu2
Fixed in–
Ubuntu 20.04 LTScythonpkg:deb/ubuntu/cython?arch=source&distro=focalOther threatsAffected
  • 0.29.10-0ubuntu1 – 0.29.14-0.1ubuntu3
6 affected builds
Fixed in–
Ubuntu 18.04 LTScythonpkg:deb/ubuntu/cython?arch=source&distro=bionicOther threatsAffected
  • =0.25.2-2build3
  • =0.26.1-0.3ubuntu1
  • =0.26.1-0.4
Fixed in–
Ubuntu 16.04 LTScythonpkg:deb/ubuntu/cython?arch=source&distro=xenialOther threatsAffected
  • 0.23.3-0ubuntu1 – 0.23.4-0ubuntu5
5 affected builds
Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

The vendor recommends migrating away from legacy all-user installers on Windows to the new Python install manager, which installs per-user and mitigates this risk. Alternative mitigations include preemptively creating and restricting access to the 'Modules' directory two levels above the Python install directory. Future Python releases will remove the fallback landmark detection, so ensuring the presence of the 'pybuilddir.txt' file is also a mitigation path.

Description

A vulnerability in Python's build system on Windows allows low-privilege users to potentially escalate privileges by creating a landmark file and alternative library folder outside the Python install directory. This occurs due to the VPATH variable pointing to a directory with weaker permissions in legacy all-user installations. The issue affects certain legacy installers and is mitigated by using the new Python install manager or restricting access to specific directories. Future Python releases will remove the fallback landmark detection that enables this behavior.

References

Community reviews

Loading reviews…