To allow builds of Python to be run from an in-tree layout (rather than an installed file layout), the VPATH variable…
Summary
Vulnerability reported (CVE-2026-12003). Risk of unauthorized operations or information disclosure. Exploitable via Lib.
Original description
The description as published by the source.
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users (in the now superseded EXE installer), due to how Windows allows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 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 esc…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-12003 has been found.
Attackers can target a specific entry point like Lib over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "CVE-2026-12003" on the vendor's site.
CVE-2026-12003 — CWE-427
Attack surface: Lib / Modules
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-427) has been reported. Attackers reach the vulnerable code path via Lib.
Check the vendor advisory for the affected versions. Attack surface: Lib / Modules.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで影響コンポーネントを特定する。
-
2Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-12003 python3.11
- Ubuntu UBUNTU-CVE-2026-12003 cython
References
- advisory https
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- patch github.com
- patch github.com
- patch github.com
- patch github.com
- patch github.com
- patch github.com
- patch github.com
- report github.com
- web https
- web github.com
- web openwall.com