From 0d328646583656a58e6c59d815e4dd1a18e69a5e Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@python.org>
Date: Thu, 10 Sep 2026 11:06:35 +0100
Subject: [PATCH] [3.12] gh-157190: Fix tarfile `data`/`tar` filter bypass via
 hard link to a symlink (GH-157191)  (GH-157192)

(cherry picked from commit 480ea4aab898291132c071645ec9ef26dab69def)
The backport to 3.13 and below includes a NEWS entry.
(cherry picked from commit b8f23e307097552eaea2604383a12ab280520d0d)

Co-authored-by: Stan Ulbrych <stan@python.org>
---
 Lib/tarfile.py                                 |  6 +++++-
 Lib/test/test_tarfile.py                       | 18 ++++++++++++++++++
 ...6-09-06-11-02-46.gh-issue-157190.tarhln.rst |  5 +++++
 3 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Security/2026-09-06-11-02-46.gh-issue-157190.tarhln.rst

diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index 13283e52b20bf55..86d47f30d99ff11 100755
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -2665,7 +2665,11 @@ def makelink_with_filter(self, tarinfo, targetpath,
                 return
             else:
                 if os.path.exists(tarinfo._link_target):
-                    os.link(tarinfo._link_target, targetpath)
+                    # Resolve the target so the hard link points to the file
+                    # itself. Otherwise os.link() may duplicate a symlink to a
+                    # shallower location, where it's relative target escapes the
+                    # destination directory. (CVE-2026-82049)
+                    os.link(os.path.realpath(tarinfo._link_target), targetpath)
                     return
         except symlink_exception:
             keyerror_to_extracterror = True
diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
index cf2c3c66561f9d7..b869fd6fa15e4c4 100644
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -4220,6 +4220,24 @@ def test_sneaky_hardlink_fallback_deep(self):
                     self.expect_file("a/b/s", symlink_to=os.path.join('..', 'escape'))
                     self.expect_file("s", symlink_to=os.path.join('..', 'escape'))
 
+    @symlink_test
+    @os_helper.skip_unless_hardlink
+    def test_sneaky_hardlink_relocation(self):
+        with ArchiveMaker() as arc:
+            arc.add("a/escape", content="decoy")
+            arc.add("a/b/s", symlink_to=os.path.join("..", "escape"))
+            arc.add("s", hardlink_to=os.path.join("a", "b", "s"))
+
+        for filter in 'data', 'tar':
+            with self.subTest(filter), self.check_context(arc.open(), filter):
+                self.expect_file("a/escape", content="decoy")
+                if os_helper.can_symlink():
+                    self.expect_file("a/b/s", symlink_to=os.path.join('..', 'escape'))
+                else:
+                    self.expect_file("a/b/s", content="decoy")
+                self.expect_file("s", content="decoy")
+                self.assertFalse((self.destdir / "s").is_symlink())
+
     @symlink_test
     def test_exfiltration_via_symlink(self):
         # (CVE-2025-4138)
diff --git a/Misc/NEWS.d/next/Security/2026-09-06-11-02-46.gh-issue-157190.tarhln.rst b/Misc/NEWS.d/next/Security/2026-09-06-11-02-46.gh-issue-157190.tarhln.rst
new file mode 100644
index 000000000000000..3dffa3bf5b5a5a8
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2026-09-06-11-02-46.gh-issue-157190.tarhln.rst
@@ -0,0 +1,5 @@
+Fixed a vulnerability in the :mod:`tarfile` ``data`` and ``tar`` extraction
+filters where a crafted archive using a hard link to a symbolic link could
+change the permissions and modification time of a file outside the
+destination directory, and expose its contents inside the extracted tree.
+This addresses :cve:`2026-82049`.