Fix CVE-2026-11940: symlink escape via tarfile hardlink fallback

Security fix for CVE-2026-11940: a symlink escape vulnerability
via tarfile hardlink-extraction fallback. The new backport patch
(00491-cve-2026-11940.patch) adds a filter check on the
hardlink's target name before performing the fallback copy,
preventing extraction of symlinks that point outside the
destination directory.

CVE: CVE-2026-11940
Upstream patches:
 - 27dd970bf6.patch
Resolves: RHEL-227194

This commit was backported by Ymir, a Red Hat Enterprise Linux software maintenance AI agent.

Assisted-by: Ymir

00492-cve-2026-11940.patch

@@ -0,0 +1,59 @@
+From a235238fe0884e85cdacbc986a4749c5c4717212 Mon Sep 17 00:00:00 2001
+From: Stan Ulbrych <stan@python.org>
+Date: Tue, 23 Jun 2026 14:31:38 +0100
+Subject: [PATCH] gh-151558: Fix symlink escape via `tarfile`
+ hardlink-extraction fallback (GH-151559)
+
+---
+ Lib/tarfile.py           |  3 +++
+ Lib/test/test_tarfile.py | 23 +++++++++++++++++++++++
+ 2 files changed, 26 insertions(+)
+
+diff --git a/Lib/tarfile.py b/Lib/tarfile.py
+index 3e03ebf..61d7e46 100755
+--- a/Lib/tarfile.py
++++ b/Lib/tarfile.py
+@@ -2642,6 +2642,9 @@ class TarFile(object):
+                     "makelink_with_filter: if filter_function is not None, "
+                     + "extraction_root must also not be None")
+             try:
++                filter_function(
++                    unfiltered.replace(name=tarinfo.name, deep=False),
++                    extraction_root)
+                 filtered = filter_function(unfiltered, extraction_root)
+             except _FILTER_ERRORS as cause:
+                 raise LinkFallbackError(tarinfo, unfiltered.name) from cause
+diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
+index 0a7586a..d43559a 100644
+--- a/Lib/test/test_tarfile.py
++++ b/Lib/test/test_tarfile.py
+@@ -3543,6 +3543,29 @@ class TestExtractionFilters(unittest.TestCase):
+                     self.expect_file("boom", symlink_to='../../link_here')
+                     self.expect_file("c", symlink_to='b')
+ 
++    def test_sneaky_hardlink_fallback_deep(self):
++        # (CVE-2026-11940)
++        with ArchiveMaker() as arc:
++            arc.add("a/b/s", symlink_to=os.path.join("..", "escape"))
++            arc.add("s", hardlink_to=os.path.join("a", "b", "s"))
++
++        with self.check_context(arc.open(), 'data'):
++            e = self.expect_exception(
++                tarfile.LinkFallbackError,
++                "link 's' would be extracted as a copy of "
++                + "'a/b/s', which was rejected")
++            self.assertIsInstance(e.__cause__,
++                                  tarfile.LinkOutsideDestinationError)
++
++        for filter in 'tar', 'fully_trusted':
++            with self.subTest(filter), self.check_context(arc.open(), filter):
++                if not support.can_symlink():
++                    self.expect_file("a/")
++                    self.expect_file("a/b/")
++                else:
++                    self.expect_file("a/b/s", symlink_to=os.path.join('..', 'escape'))
++                    self.expect_file("s", symlink_to=os.path.join('..', 'escape'))
++
+     def test_exfiltration_via_symlink(self):
+         # (CVE-2025-4138)
+         # Test changing symlinks that result in a symlink pointing outside

python3.spec

@@ -14,7 +14,7 @@ URL: https://www.python.org/
 #  WARNING  When rebasing to a new Python version,
 #           remember to update the python3-docs package as well
 Version: %{pybasever}.8
-Release: 77%{?dist}
+Release: 78%{?dist}
 License: Python
 
 
@@ -1028,6 +1028,12 @@ Patch482: 00482-cve-2026-6100.patch
 # only joined and parsed once enough has piled up.
 Patch490: 00490-cve-2026-15308.patch
 
+# 00492 #
+# CVE-2026-11940
+#
+# gh-151558: Fix symlink escape via tarfile hardlink-extraction fallback (GH-151559)
+Patch492: 00492-cve-2026-11940.patch
+
 # (New patches go here ^^^)
 #
 # When adding new patches to "python" and "python3" in Fedora, EL, etc.,
@@ -1409,6 +1415,7 @@ GIT_DIR=$PWD git apply %{PATCH351}
 %patch480 -p1
 %patch482 -p1
 %patch490 -p1
+%patch492 -p1
 
 # Remove files that should be generated by the build
 # (This is after patching, so that we can use patches directly from upstream)
@@ -2340,6 +2347,10 @@ fi
 # ======================================================
 
 %changelog
+* Thu Aug 06 2026 RHEL Packaging Agent <redhat-ymir-agent@redhat.com> - 3.6.8-78
+- Security fix for CVE-2026-11940
+Resolves: RHEL-227194
+
 * Fri Jul 10 2026 Lumír Balhar <lbalhar@redhat.com> - 3.6.8-77
 - Security fix for CVE-2026-15308
 Resolves: RHEL-193772