https://github.com/python/cpython/commit/9e863fab283eddca9c2a8f9d1ee30f4dc243e314
commit: 9e863fab283eddca9c2a8f9d1ee30f4dc243e314
branch: main
author: Steve Dower <[email protected]>
committer: zooba <[email protected]>
date: 2026-06-17T00:16:06+01:00
summary:
gh-151544: Fixes CVE-2026-12003 by removing the fallback to
%VPATH%/Modules/Setup.local for discovering sources in getpath.py (GH-151545)
files:
A Misc/NEWS.d/next/Security/2026-06-16-14-58-02.gh-issue-151544._bexVy.rst
M Makefile.pre.in
M Modules/getpath.py
diff --git a/Makefile.pre.in b/Makefile.pre.in
index 2b34b009fd745a0..cf700e9f2340901 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -1616,6 +1616,8 @@ Programs/_bootstrap_python.o:
Programs/_bootstrap_python.c $(BOOTSTRAP_HEADERS)
_bootstrap_python: $(LIBRARY_OBJS_OMIT_FROZEN) Programs/_bootstrap_python.o
Modules/getpath.o Modules/Setup.local
$(LINKCC) $(PY_LDFLAGS_NOLTO) -o $@ $(LIBRARY_OBJS_OMIT_FROZEN) \
Programs/_bootstrap_python.o Modules/getpath.o $(LIBS)
$(MODLIBS) $(SYSLIBS)
+ # Dummy pybuilddir.txt is needed for _bootstrap_python to be runnable
+ @echo "none" > ./pybuilddir.txt
############################################################################
diff --git
a/Misc/NEWS.d/next/Security/2026-06-16-14-58-02.gh-issue-151544._bexVy.rst
b/Misc/NEWS.d/next/Security/2026-06-16-14-58-02.gh-issue-151544._bexVy.rst
new file mode 100644
index 000000000000000..418e3b4b9677943
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2026-06-16-14-58-02.gh-issue-151544._bexVy.rst
@@ -0,0 +1,4 @@
+:file:`Modules/Setup.local` is no longer used as a landmark to discover
+whether Python is running in a source tree, as it could potentially affect
+actual installs. The :file:`pybuilddir.txt` file is now the sole indicator
+of running in a source tree.
diff --git a/Modules/getpath.py b/Modules/getpath.py
index 4dceb5cdc8dfcf0..6199567bd777aa0 100644
--- a/Modules/getpath.py
+++ b/Modules/getpath.py
@@ -129,8 +129,7 @@
# checked by looking for the BUILDDIR_TXT file, which contains the
# relative path to the platlib dir. The executable_dir value is
# derived from joining the VPATH preprocessor variable to the
-# directory containing pybuilddir.txt. If it is not found, the
-# BUILD_LANDMARK file is found, which is part of the source tree.
+# directory containing pybuilddir.txt.
# prefix is then found by searching up for a file that should only
# exist in the source tree, and the stdlib dir is set to prefix/Lib.
@@ -177,7 +176,6 @@
if os_name == 'posix' or os_name == 'darwin':
BUILDDIR_TXT = 'pybuilddir.txt'
- BUILD_LANDMARK = 'Modules/Setup.local'
DEFAULT_PROGRAM_NAME = f'python{VERSION_MAJOR}'
STDLIB_SUBDIR =
f'{platlibdir}/python{VERSION_MAJOR}.{VERSION_MINOR}{ABI_THREAD}'
STDLIB_LANDMARKS = [f'{STDLIB_SUBDIR}/os.py', f'{STDLIB_SUBDIR}/os.pyc']
@@ -190,7 +188,6 @@
elif os_name == 'nt':
BUILDDIR_TXT = 'pybuilddir.txt'
- BUILD_LANDMARK = f'{VPATH}\\Modules\\Setup.local'
DEFAULT_PROGRAM_NAME = f'python'
STDLIB_SUBDIR = 'Lib'
STDLIB_LANDMARKS = [f'{STDLIB_SUBDIR}\\os.py', f'{STDLIB_SUBDIR}\\os.pyc']
@@ -513,13 +510,9 @@ def search_up(prefix, *landmarks, test=isfile):
platstdlib_dir = real_executable_dir
build_prefix = joinpath(real_executable_dir, VPATH)
except (FileNotFoundError, PermissionError):
- if isfile(joinpath(real_executable_dir, BUILD_LANDMARK)):
- build_prefix = joinpath(real_executable_dir, VPATH)
- if os_name == 'nt':
- # QUIRK: Windows builds need platstdlib_dir to be the
executable
- # dir. Normally the builddir marker handles this, but in this
- # case we need to correct manually.
- platstdlib_dir = real_executable_dir
+ # We used to check for an alternate landmark here, but now we require
+ # BUILDDIR_TXT to exist. (gh-151544; CVE-2026-12003)
+ pass
if build_prefix:
if os_name == 'nt':
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