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gh-149835: _destinsrc to use realpath instead of abspath #149986

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gh-149835: _destinsrc to use realpath instead of abspath #149986

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4e5bd4e
fix: _destinsrc to use realpath instead of abspath
KowalskiThomas May 13, 2026
3147bc5
misc: add news entry
KowalskiThomas May 18, 2026
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4 changes: 2 additions & 2 deletions Lib/shutil.py
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Original file line number Diff line number Diff line change
Expand Up @@ -940,8 +940,8 @@ def move(src, dst, copy_function=copy2):
return real_dst

def _destinsrc(src, dst):
src = os.path.abspath(src)
dst = os.path.abspath(dst)
src = os.path.realpath(src)
dst = os.path.realpath(dst)
if not src.endswith(os.path.sep):
src += os.path.sep
if not dst.endswith(os.path.sep):
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17 changes: 17 additions & 0 deletions Lib/test/test_shutil.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2914,6 +2914,23 @@ def test_destinsrc_false_positive(self):
finally:
os_helper.rmtree(TESTFN)

@os_helper.skip_unless_symlink
def test_destinsrc_symlink_bypass(self):
tmp = self.mkdtemp()
src = os.path.join(tmp, 'src')
os.makedirs(src)
# tmp/link -> tmp (one level up)
link = os.path.join(tmp, 'link')
os.symlink(tmp, link)
# raw path: tmp/link/src/sub - no src prefix in string space
# real path: tmp/src/sub - physically inside src
dst = os.path.join(link, 'src', 'sub')
self.assertTrue(
shutil._destinsrc(src, dst),
msg='_destinsrc failed to detect dst inside src via symlink '
'(dst=%s, src=%s)' % (dst, src),
)

@os_helper.skip_unless_symlink
@mock_rename
def test_move_file_symlink(self):
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Security/2026-05-18-17-46-00.gh-issue-149835.EebFlk.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
:func:`shutil.move` now resolves symlinks via :func:`os.path.realpath`
when checking whether the destination is inside the source directory,
preventing a symlink-based bypass of that guard.
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