diff -Nru python-apt-1.9.0ubuntu1.2/apt/cache.py python-apt-1.9.0ubuntu1.3/apt/cache.py
--- python-apt-1.9.0ubuntu1.2/apt/cache.py	2020-01-15 15:35:02.000000000 +0000
+++ python-apt-1.9.0ubuntu1.3/apt/cache.py	2020-01-22 21:47:41.000000000 +0000
@@ -456,7 +456,7 @@
     def _fetch_archives(self,
                         fetcher,                # type: apt_pkg.Acquire
                         pm,                     # type: apt_pkg.PackageManager
-                        allow_unauthenticated,  # type: Optional[bool]
+                        allow_unauthenticated=None,  # type: Optional[bool]
                         ):
         # type: (...) -> int
         """ fetch the needed archives """
diff -Nru python-apt-1.9.0ubuntu1.2/debian/changelog python-apt-1.9.0ubuntu1.3/debian/changelog
--- python-apt-1.9.0ubuntu1.2/debian/changelog	2020-01-15 15:35:02.000000000 +0000
+++ python-apt-1.9.0ubuntu1.3/debian/changelog	2020-01-22 21:47:49.000000000 +0000
@@ -1,3 +1,11 @@
+python-apt (1.9.0ubuntu1.3) eoan-security; urgency=medium
+
+  * SECURITY REGRESSION: crash with ubuntu-release-upgrader (LP: #1860606)
+    - apt/cache.py: make allow_unauthenticated argument to
+      fetch_archives() optional.
+
+ -- Marc Deslauriers <marc.deslauriers@ubuntu.com>  Wed, 22 Jan 2020 16:47:49 -0500
+
 python-apt (1.9.0ubuntu1.2) eoan-security; urgency=medium
 
   * SECURITY UPDATE: Check that repository is trusted before downloading