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/f7666e828cc3d5873136473ea36ba2013d624fa1

diff --git Include/pyexpat.h Include/pyexpat.h
index 44259bf6d7..07020b5dc9 100644
--- Include/pyexpat.h
+++ 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
@@ -48,6 +48,8 @@ struct PyExpat_CAPI
     enum XML_Status (*SetEncoding)(XML_Parser parser, const XML_Char *encoding);
     int (*DefaultUnknownEncodingHandler)(
         void *encodingHandlerData, const XML_Char *name, XML_Encoding *info);
+    /* 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 Modules/_elementtree.c Modules/_elementtree.c
index 707ab2912b..53f05f937f 100644
--- Modules/_elementtree.c
+++ Modules/_elementtree.c
@@ -3261,6 +3261,11 @@ _elementtree_XMLParser___init___impl(XMLParserObject *self, PyObject *html,
         PyErr_NoMemory();
         return -1;
     }
+    /* expat < 2.1.0 has no XML_SetHashSalt() */
+    if (EXPAT(SetHashSalt) != NULL) {
+        EXPAT(SetHashSalt)(self->parser,
+                           (unsigned long)_Py_HashSecret.expat.hashsalt);
+    }
 
     if (target) {
         Py_INCREF(target);
diff --git Modules/pyexpat.c Modules/pyexpat.c
index 47c3e86c20..aa21d93c11 100644
--- Modules/pyexpat.c
+++ Modules/pyexpat.c
@@ -1887,6 +1887,11 @@ MODULE_INITFUNC(void)
     capi.SetStartDoctypeDeclHandler = XML_SetStartDoctypeDeclHandler;
     capi.SetEncoding = XML_SetEncoding;
     capi.DefaultUnknownEncodingHandler = PyUnknownEncodingHandler;
+#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);
?id=5b5c50961fc3c2c95cb97796369ec918cbff064f'>build-aux</a>/<a href='/guix/log/build-aux/test-driver.scm?id=5b5c50961fc3c2c95cb97796369ec918cbff064f'>test-driver.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/build-aux/test-driver.scm?id=5b5c50961fc3c2c95cb97796369ec918cbff064f&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-02-02 00:28:49 -0500'>2021-02-02</span></td><td><a href='/guix/commit/build-aux/test-driver.scm?id=5e652e94a9203e0cfa27e93a89878439b7900001'>build: Add a --show-duration option to the SCM test-driver.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-01-31 22:28:46 -0500'>2021-01-31</span></td><td><a href='/guix/commit/build-aux/test-driver.scm?id=26a66d0feaab7626c4053071d5557394931fe14b'>build: test-driver.scm: Allow running as a standalone script.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-01-31 22:28:46 -0500'>2021-01-31</span></td><td><a href='/guix/commit/build-aux/test-driver.scm?id=93a628c4e4f4a7f6665190f3c52a417daebaf28a'>build: test-driver.scm: Add a new '--errors-only' option.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-01-31 22:28:37 -0500'>2021-01-31</span></td><td><a href='/guix/commit/build-aux/test-driver.scm?id=a1ea2acb376c8a74f41ce0e683680417207b365a'>build: test-driver.scm: Add test cases filtering options.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-01-31 22:23:41 -0500'>2021-01-31</span></td><td><a href='/guix/commit/build-aux/test-driver.scm?id=346210b1b2130112dd5f894c1d40afb37c1c51a5'>build: test-driver.scm: Enable colored test results by default.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-01-31 22:23:41 -0500'>2021-01-31</span></td><td><a href='/guix/commit/build-aux/test-driver.scm?id=13f299b2c98cce0ede3a8a37dd11832fdb3827bb'>build: test-driver.scm: Make output redirection optional.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>