Fix CVE-2018-14647:
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-14647
https://bugs.python.org/issue34623

Taken from upstream:
https://github.com/python/cpython/commit/18b20bad75b4ff0486940fba4ec680e96e70f3a2

diff --git a/Include/pyexpat.h b/Include/pyexpat.h
index 5340ef5fa3..3fc5fa54da 100644
--- a/Include/pyexpat.h
+++ b/Include/pyexpat.h
@@ -3,7 +3,7 @@
 
 /* note: you must import expat.h before importing this module! */
 
-#define PyExpat_CAPI_MAGIC  "pyexpat.expat_CAPI 1.0"
+#define PyExpat_CAPI_MAGIC  "pyexpat.expat_CAPI 1.1"
 #define PyExpat_CAPSULE_NAME "pyexpat.expat_CAPI"
 
 struct PyExpat_CAPI 
@@ -43,6 +43,8 @@ struct PyExpat_CAPI
         XML_Parser parser, XML_UnknownEncodingHandler handler,
         void *encodingHandlerData);
     void (*SetUserData)(XML_Parser parser, void *userData);
+    /* might be none for expat < 2.1.0 */
+    int (*SetHashSalt)(XML_Parser parser, unsigned long hash_salt);
     /* always add new stuff to the end! */
 };
 
diff --git a/Modules/_elementtree.c b/Modules/_elementtree.c
index f7f992dd3a..b38e0ab329 100644
--- a/Modules/_elementtree.c
+++ b/Modules/_elementtree.c
@@ -2574,6 +2574,11 @@ xmlparser(PyObject* self_, PyObject* args, PyObject* kw)
         PyErr_NoMemory();
         return NULL;
     }
+    /* expat < 2.1.0 has no XML_SetHashSalt() */
+    if (EXPAT(SetHashSalt) != NULL) {
+        EXPAT(SetHashSalt)(self->parser,
+                           (unsigned long)_Py_HashSecret.prefix);
+    }
 
     ALLOC(sizeof(XMLParserObject), "create expatparser");
 
diff --git a/Modules/pyexpat.c b/Modules/pyexpat.c
index 2b4d31293c..1f8c0d70a5 100644
--- a/Modules/pyexpat.c
+++ b/Modules/pyexpat.c
@@ -2042,6 +2042,11 @@ MODULE_INITFUNC(void)
     capi.SetProcessingInstructionHandler = XML_SetProcessingInstructionHandler;
     capi.SetUnknownEncodingHandler = XML_SetUnknownEncodingHandler;
     capi.SetUserData = XML_SetUserData;
+#if XML_COMBINED_VERSION >= 20100
+    capi.SetHashSalt = XML_SetHashSalt;
+#else
+    capi.SetHashSalt = NULL;
+#endif
 
     /* export using capsule */
     capi_object = PyCapsule_New(&capi, PyExpat_CAPSULE_NAME, NULL);
/<a href='/guix/log/gnu?id=170436771968dfa272225ea45b63689b900fd317'>gnu</a>/<a href='/guix/log/gnu/packages?id=170436771968dfa272225ea45b63689b900fd317'>packages</a>/<a href='/guix/log/gnu/packages/patchutils.scm?id=170436771968dfa272225ea45b63689b900fd317'>patchutils.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/patchutils.scm?id=170436771968dfa272225ea45b63689b900fd317&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2018-12-05 00:08:28 +0100'>2018-12-05</span></td><td><a href='/guix/commit/gnu/packages/patchutils.scm?id=c16c119d0a7894c42bbe816ec381a0f458f26e6a'>gnu: quilt: Use shorter file names for patches.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-11-30 00:21:25 -0600'>2018-11-30</span></td><td><a href='/guix/commit/gnu/packages/patchutils.scm?id=5f230fb2798e9862fba67228b9de89df8f36e8e0'>patchutils: Update to 0.3.4.</a><span class='msg-avail'>...</span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2018-10-03 10:45:02 -0500'>2018-10-03</span></td><td><a href='/guix/commit/gnu/packages/patchutils.scm?id=43eb42ef017aa4752503fb2913781bb446716c1e'>quilt: Remove test workarounds.</a><span class='msg-avail'>...</span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2018-10-02 22:34:44 -0500'>2018-10-02</span></td><td><a href='/guix/commit/gnu/packages/patchutils.scm?id=d7d1fc821091de98d66dac71ceed390d82434e40'>quilt: Add diffstat input.</a><span class='msg-avail'>...</span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2018-10-02 22:34:44 -0500'>2018-10-02</span></td><td><a href='/guix/commit/gnu/packages/patchutils.scm?id=24a80064ca7faf504563af33217e07372285fb2f'>quilt: Install translations.</a><span class='msg-avail'>...</span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2018-10-02 22:34:39 -0500'>2018-10-02</span></td><td><a href='/guix/commit/gnu/packages/patchutils.scm?id=68faa20e2d4511b43062f8279cc407aee735b275'>quilt: Upgrade to 0.65.</a><span class='msg-avail'>...</span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2018-08-09 08:07:35 -0400'>2018-08-09</span></td><td><a href='/guix/commit/gnu/packages/patchutils.scm?id=9e286eb1b55989cd171e61b3943c1e51545930ad'>gnu: Add VBinDiff.</a><span class='msg-avail'>...</span></td><td>Leo Famulari</td></tr>
<tr><td><span title='2018-01-12 13:08:13 +0100'>2018-01-12</span></td><td><a href='/guix/commit/gnu/packages/patchutils.scm?id=58e3603e7f5452026b9a5fa61bb771d153ead4f4'>gnu: colordiff: Update to 1.0.18.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2017-10-20 02:16:54 +0200'>2017-10-20</span></td><td><a href='/guix/commit/gnu/packages/patchutils.scm?id=8cccd09d3e27c3b475fd559ea1bae5f843a26bbe'>gnu: colordiff: Use HTTPS home page.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2017-09-20 20:58:04 -0400'>2017-09-20</span></td><td><a href='/guix/commit/gnu/packages/patchutils.scm?id=dc1d3cdef70f0e3c047c229c2a0e561d1f47bde8'>gnu: Use 'modify-phases' syntax.</a><span class='msg-avail'>...</span></td><td>Kei Kebreau</td></tr>