commit 5c47ae80738d0985babf06a023b3845169682064
Author: Tomas Korbar <tkorbar@redhat.com>
Date: Mon Mar 14 10:22:37 2022 +0100
Protect against malicious namespace declarations
diff --git a/lib/xmlparse.c b/lib/xmlparse.c
index 5c3f573..901abbf 100644
--- a/lib/xmlparse.c
+++ b/lib/xmlparse.c
@@ -638,8 +638,7 @@ XML_ParserCreate(const XML_Char *encodingName) {
XML_Parser XMLCALL
XML_ParserCreateNS(const XML_Char *encodingName, XML_Char nsSep) {
- XML_Char tmp[2];
- *tmp = nsSep;
+ XML_Char tmp[2] = {nsSep, 0};
return XML_ParserCreate_MM(encodingName, NULL, tmp);
}
@@ -1253,8 +1252,7 @@ XML_ExternalEntityParserCreate(XML_Parser oldParser, const XML_Char *context,
would be otherwise.
*/
if (parser->m_ns) {
- XML_Char tmp[2];
- *tmp = parser->m_namespaceSeparator;
+ XML_Char tmp[2] = {parser->m_namespaceSeparator, 0};
parser = parserCreate(encodingName, &parser->m_mem, tmp, newDtd);
} else {
parser = parserCreate(encodingName, &parser->m_mem, NULL, newDtd);
@@ -3526,6 +3524,117 @@ storeAtts(XML_Parser parser, const ENCODING *enc, const char *attStr,
return XML_ERROR_NONE;
}
+static XML_Bool
+is_rfc3986_uri_char(XML_Char candidate) {
+ // For the RFC 3986 ANBF grammar see
+ // https://datatracker.ietf.org/doc/html/rfc3986#appendix-A
+
+ switch (candidate) {
+ // From rule "ALPHA" (uppercase half)
+ case 'A':
+ case 'B':
+ case 'C':
+ case 'D':
+ case 'E':
+ case 'F':
+ case 'G':
+ case 'H':
+ case 'I':
+ case 'J':
+ case 'K':
+ case 'L':
+ case 'M':
+ case 'N':
+ case 'O':
+ case 'P':
+ case 'Q':
+ case 'R':
+ case 'S':
+ case 'T':
+ case 'U':
+ case 'V':
+ case 'W':
+ case 'X':
+ case 'Y':
+ case 'Z':
+
+ // From rule "ALPHA" (lowercase half)
+ case 'a':
+ case 'b':
+ case 'c':
+ case 'd':
+ case 'e':
+ case 'f':
+ case 'g':
+ case 'h':
+ case 'i':
+ case 'j':
+ case 'k':
+ case 'l':
+ case 'm':
+ case 'n':
+ case 'o':
+ case 'p':
+ case 'q':
+ case 'r':
+ case 's':
+ case 't':
+ case 'u':
+ case 'v':
+ case 'w':
+ case 'x':
+ case 'y':
+ case 'z':
+
+ // From rule "DIGIT"
+ case '0':
+ case '1':
+ case '2':
+ case '3':
+ case '4':
+ case '5':
+ case '6':
+ case '7':
+ case '8':
+ case '9':
+
+ // From rule "pct-encoded"
+ case '%':
+
+ // From rule "unreserved"
+ case '-':
+ case '.':
+ case '_':
+ case '~':
+
+ // From rule "gen-delims"
+ case ':':
+ case '/':
+ case '?':
+ case '#':
+ case '[':
+ case ']':
+ case '@':
+
+ // From rule "sub-delims"
+ case '!':
+ case '$':
+ case '&':
+ case '\'':
+ case '(':
+ case ')':
+ case '*':
+ case '+':
+ case ',':
+ case ';':
+ case '=':
+ return XML_TRUE;
+
+ default:
+ return XML_FALSE;
+ }
+}
+
/* addBinding() overwrites the value of prefix->binding without checking.
Therefore one must keep track of the old value outside of addBinding().
*/
@@ -3581,6 +3690,29 @@ addBinding(XML_Parser parser, PREFIX *prefix, const ATTRIBUTE_ID *attId,
if (! mustBeXML && isXMLNS
&& (len > xmlnsLen || uri[len] != xmlnsNamespace[len]))
isXMLNS = XML_FALSE;
+
+ // NOTE: While Expat does not validate namespace URIs against RFC 3986
+ // today (and is not REQUIRED to do so with regard to the XML 1.0
+ // namespaces specification) we have to at least make sure, that
+ // the application on top of Expat (that is likely splitting expanded
+ // element names ("qualified names") of form
+ // "[uri sep] local [sep prefix] '\0'" back into 1, 2 or 3 pieces
+ // in its element handler code) cannot be confused by an attacker
+ // putting additional namespace separator characters into namespace
+ // declarations. That would be ambiguous and not to be expected.
+ //
+ // While the HTML API docs of function XML_ParserCreateNS have been
+ // advising against use of a namespace separator character that can
+ // appear in a URI for >20 years now, some widespread applications
+ // are using URI characters (':' (colon) in particular) for a
+ // namespace separator, in practice. To keep these applications
+ // functional, we only reject namespaces URIs containing the
+ // application-chosen namespace separator if the chosen separator
+ // is a non-URI character with regard to RFC 3986.
+ if (parser->m_ns && (uri[len] == parser->m_namespaceSeparator)
+ && ! is_rfc3986_uri_char(uri[len])) {
+ return XML_ERROR_SYNTAX;
+ }
}
isXML = isXML && len == xmlLen;
isXMLNS = isXMLNS && len == xmlnsLen;
diff --git a/tests/runtests.c b/tests/runtests.c
index f03e008..40172d2 100644
--- a/tests/runtests.c
+++ b/tests/runtests.c
@@ -7233,6 +7233,37 @@ START_TEST(test_ns_double_colon_doctype) {
}
END_TEST
+START_TEST(test_ns_separator_in_uri) {
+ struct test_case {
+ enum XML_Status expectedStatus;
+ const char *doc;
+ XML_Char namesep;
+ };
+ struct test_case cases[] = {
+ {XML_STATUS_OK, "<doc xmlns='one_two' />", XCS('\n')},
+ {XML_STATUS_ERROR, "<doc xmlns='one
two' />", XCS('\n')},
+ {XML_STATUS_OK, "<doc xmlns='one:two' />", XCS(':')},
+ };
+
+ size_t i = 0;
+ size_t failCount = 0;
+ for (; i < sizeof(cases) / sizeof(cases[0]); i++) {
+ XML_Parser parser = XML_ParserCreateNS(NULL, cases[i].namesep);
+ XML_SetElementHandler(parser, dummy_start_element, dummy_end_element);
+ if (XML_Parse(parser, cases[i].doc, (int)strlen(cases[i].doc),
+ /*isFinal*/ XML_TRUE)
+ != cases[i].expectedStatus) {
+ failCount++;
+ }
+ XML_ParserFree(parser);
+ }
+
+ if (failCount) {
+ fail("Namespace separator handling is broken");
+ }
+}
+END_TEST
+
/* Control variable; the number of times duff_allocator() will successfully
* allocate */
#define ALLOC_ALWAYS_SUCCEED (-1)
@@ -11527,6 +11558,7 @@ make_suite(void) {
tcase_add_test(tc_namespace, test_ns_utf16_doctype);
tcase_add_test(tc_namespace, test_ns_invalid_doctype);
tcase_add_test(tc_namespace, test_ns_double_colon_doctype);
+ tcase_add_test(tc_namespace, test_ns_separator_in_uri);
suite_add_tcase(s, tc_misc);
tcase_add_checked_fixture(tc_misc, NULL, basic_teardown);