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From 2ba6c76fca21397959145e18c5ef376201209020 Mon Sep 17 00:00:00 2001 |
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From: Sebastian Pipping <sebastian@pipping.org> |
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Date: Sun, 27 Feb 2022 16:58:08 +0100 |
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Subject: [PATCH] lib: Relax fix to CVE-2022-25236 with regard to RFC 3986 URI |
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characters |
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|
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--- |
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expat/lib/xmlparse.c | 139 ++++++++++++++++++++++++++++++++++++++++--- |
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1 file changed, 131 insertions(+), 8 deletions(-) |
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|
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--- a/lib/xmlparse.c |
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+++ b/lib/xmlparse.c |
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@@ -3512,6 +3512,117 @@ storeAtts(XML_Parser parser, const ENCOD |
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return XML_ERROR_NONE; |
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} |
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|
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+static XML_Bool |
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+is_rfc3986_uri_char(XML_Char candidate) { |
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+ // For the RFC 3986 ANBF grammar see |
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+ // https://datatracker.ietf.org/doc/html/rfc3986#appendix-A |
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+ |
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+ switch (candidate) { |
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+ // From rule "ALPHA" (uppercase half) |
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+ case 'A': |
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+ case 'B': |
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+ case 'C': |
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+ case 'D': |
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+ case 'E': |
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+ case 'F': |
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+ case 'G': |
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+ case 'H': |
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+ case 'I': |
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+ case 'J': |
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+ case 'K': |
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+ case 'L': |
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+ case 'M': |
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+ case 'N': |
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+ case 'O': |
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+ case 'P': |
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+ case 'Q': |
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+ case 'R': |
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+ case 'S': |
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+ case 'T': |
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+ case 'U': |
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+ case 'V': |
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+ case 'W': |
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+ case 'X': |
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+ case 'Y': |
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+ case 'Z': |
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+ |
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+ // From rule "ALPHA" (lowercase half) |
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+ case 'a': |
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+ case 'b': |
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+ case 'c': |
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+ case 'd': |
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+ case 'e': |
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+ case 'f': |
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+ case 'g': |
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+ case 'h': |
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+ case 'i': |
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+ case 'j': |
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+ case 'k': |
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+ case 'l': |
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+ case 'm': |
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+ case 'n': |
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+ case 'o': |
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+ case 'p': |
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+ case 'q': |
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+ case 'r': |
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+ case 's': |
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+ case 't': |
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+ case 'u': |
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+ case 'v': |
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+ case 'w': |
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+ case 'x': |
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+ case 'y': |
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+ case 'z': |
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+ |
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+ // From rule "DIGIT" |
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+ case '0': |
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+ case '1': |
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+ case '2': |
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+ case '3': |
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+ case '4': |
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+ case '5': |
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+ case '6': |
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+ case '7': |
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+ case '8': |
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+ case '9': |
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+ |
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+ // From rule "pct-encoded" |
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+ case '%': |
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+ |
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+ // From rule "unreserved" |
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+ case '-': |
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+ case '.': |
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+ case '_': |
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+ case '~': |
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+ |
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+ // From rule "gen-delims" |
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+ case ':': |
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+ case '/': |
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+ case '?': |
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+ case '#': |
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+ case '[': |
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+ case ']': |
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+ case '@': |
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+ |
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+ // From rule "sub-delims" |
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+ case '!': |
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+ case '$': |
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+ case '&': |
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+ case '\'': |
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+ case '(': |
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+ case ')': |
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+ case '*': |
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+ case '+': |
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+ case ',': |
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+ case ';': |
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+ case '=': |
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+ return XML_TRUE; |
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+ |
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+ default: |
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+ return XML_FALSE; |
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+ } |
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+} |
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+ |
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/* addBinding() overwrites the value of prefix->binding without checking. |
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Therefore one must keep track of the old value outside of addBinding(). |
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*/ |
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@@ -3568,14 +3679,26 @@ addBinding(XML_Parser parser, PREFIX *pr |
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&& (len > xmlnsLen || uri[len] != xmlnsNamespace[len])) |
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isXMLNS = XML_FALSE; |
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|
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- // NOTE: While Expat does not validate namespace URIs against RFC 3986, |
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- // we have to at least make sure that the XML processor on top of |
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- // Expat (that is splitting tag names by namespace separator into |
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- // 2- or 3-tuples (uri-local or uri-local-prefix)) cannot be confused |
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- // by an attacker putting additional namespace separator characters |
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- // into namespace declarations. That would be ambiguous and not to |
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- // be expected. |
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- if (parser->m_ns && (uri[len] == parser->m_namespaceSeparator)) { |
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+ // NOTE: While Expat does not validate namespace URIs against RFC 3986 |
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+ // today (and is not REQUIRED to do so with regard to the XML 1.0 |
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+ // namespaces specification) we have to at least make sure, that |
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+ // the application on top of Expat (that is likely splitting expanded |
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+ // element names ("qualified names") of form |
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+ // "[uri sep] local [sep prefix] '\0'" back into 1, 2 or 3 pieces |
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+ // in its element handler code) cannot be confused by an attacker |
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+ // putting additional namespace separator characters into namespace |
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+ // declarations. That would be ambiguous and not to be expected. |
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+ // |
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+ // While the HTML API docs of function XML_ParserCreateNS have been |
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+ // advising against use of a namespace separator character that can |
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+ // appear in a URI for >20 years now, some widespread applications |
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+ // are using URI characters (':' (colon) in particular) for a |
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+ // namespace separator, in practice. To keep these applications |
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+ // functional, we only reject namespaces URIs containing the |
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+ // application-chosen namespace separator if the chosen separator |
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+ // is a non-URI character with regard to RFC 3986. |
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+ if (parser->m_ns && (uri[len] == parser->m_namespaceSeparator) |
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+ && ! is_rfc3986_uri_char(uri[len])) { |
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return XML_ERROR_SYNTAX; |
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} |
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} |
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