CVE-2026-12003: Python Software Foundation CPython · Uncontrolled Search Path Element
Affects Python Software Foundation CPythonSource CVE Database V5
Not known to be exploited · CVSS 5.3 Medium · fixed in 3.15.0b3 : update Python Software Foundation CPython when convenient.
Data as of 30 Oct 2026, 20:25 UTC
- EPSS
- 0.1% chance of exploitation in 30 days – higher than 3% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 3.15.0b3, 3.14.7, 3.13.15 +2
CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:NExploitation evidence
Disclosed: evidence found.
CVE published 16 Jun 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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 30 Oct 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| Python Software FoundationCPython | Affected
| Fixed in
|
| Python Software FoundationCPython | Affected
| Fixed in
|
| Python Software FoundationCPython | Affected
| Fixed in
|
| Python Software FoundationCPython | Affected
| Fixed in
|
| Python Software FoundationCPython | Affected
| Fixed in
|
GitHubCPythonpkg:github/CPythonOther threats | Affected
| 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 Python Software Foundation recommends migrating away from the legacy EXE installer on Windows to the new Python install manager, which installs Python per-user and restricts modification by other users, effectively mitigating the risk. Alternatively, administrators can preemptively create and restrict access to the Modules directory two levels above the Python install directory to prevent unauthorized creation of landmarks. Future Python releases will remove the fallback landmark detection that relies on VPATH, requiring builds to generate or preserve the pybuilddir.txt file.
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.
References
- github.com/python/cpython/pull/151545 (opens in a new tab)
- github.com/python/cpython/issues/151544 (opens in a new tab)
- https//mail.python.org/archives/list/security-announce@python.org/thread/JIFOBO7UX3LY4VJKJUOKYJV62CFR2IRH/ (opens in a new tab)
- github.com/python/cpython/commit/16c40f944b7bff724a403cf4902763d095bb4b2a (opens in a new tab)
- github.com/python/cpython/commit/9e863fab283eddca9c2a8f9d1ee30f4dc243e314 (opens in a new tab)
- github.com/python/cpython/commit/a86de0bc236fbb9452f98998fc8437e9fca35700 (opens in a new tab)
- github.com/python/cpython/commit/b93d6d3399adbd3a5037b6b92fc3587c85ac5d56 (opens in a new tab)
- openwall.com/lists/oss-security/2026/06/16/8 (opens in a new tab)
- github.com/python/cpython/commit/03ab7b44788bfd6b8927e16bcdbd025aa08dce06 (opens in a new tab)
- github.com/python/cpython/commit/872038377db2e170e0e140b5f8aaedf636b3fbf5 (opens in a new tab)