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Prevent access to external files/URLs via contrib/xml2's xslt_process().

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libxslt offers the ability to read and write both files and URLs through
stylesheet commands, thus allowing unprivileged database users to both read
and write data with the privileges of the database server.  Disable that
through proper use of libxslt's security options.

Also, remove xslt_process()'s ability to fetch documents and stylesheets
from external files/URLs.  While this was a documented "feature", it was
long regarded as a terrible idea.  The fix for CVE-2012-3489 broke that
capability, and rather than expend effort on trying to fix it, we're just
going to summarily remove it.

While the ability to write as well as read makes this security hole
considerably worse than CVE-2012-3489, the problem is mitigated by the fact
that xslt_process() is not available unless contrib/xml2 is installed,
and the longstanding warnings about security risks from that should have
discouraged prudent DBAs from installing it in security-exposed databases.

Reported and fixed by Peter Eisentraut.

Security: CVE-2012-3488
This commit is contained in:
Tom Lane
2012-08-14 18:28:53 -04:00
parent a34e02bfaf
commit d9b023c7bc
5 changed files with 103 additions and 29 deletions
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15
contrib/xml2/expected/xml2.out
View File

@ -145,3 +145,18 @@ values
Value</attribute></attributes>');
create index idx_xpath on t1 ( xpath_string
('/attributes/attribute[@name="attr_1"]/text()', xml_data::text));
-- possible security exploit
SELECT xslt_process('<xml><foo>Hello from XML</foo></xml>',
$$<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:sax="http://icl.com/saxon"
extension-element-prefixes="sax">
<xsl:template match="//foo">
<sax:output href="0wn3d.txt" method="text">
<xsl:value-of select="'0wn3d via xml2 extension and libxslt'"/>
<xsl:apply-templates/>
</sax:output>
</xsl:template>
</xsl:stylesheet>$$);
ERROR: failed to apply stylesheet

15
contrib/xml2/expected/xml2_1.out
View File

@ -107,3 +107,18 @@ values
Value</attribute></attributes>');
create index idx_xpath on t1 ( xpath_string
('/attributes/attribute[@name="attr_1"]/text()', xml_data::text));
-- possible security exploit
SELECT xslt_process('<xml><foo>Hello from XML</foo></xml>',
$$<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:sax="http://icl.com/saxon"
extension-element-prefixes="sax">
<xsl:template match="//foo">
<sax:output href="0wn3d.txt" method="text">
<xsl:value-of select="'0wn3d via xml2 extension and libxslt'"/>
<xsl:apply-templates/>
</sax:output>
</xsl:template>
</xsl:stylesheet>$$);
ERROR: xslt_process() is not available without libxslt

15
contrib/xml2/sql/xml2.sql
View File

@ -80,3 +80,18 @@ Value</attribute></attributes>');
create index idx_xpath on t1 ( xpath_string
('/attributes/attribute[@name="attr_1"]/text()', xml_data::text));
-- possible security exploit
SELECT xslt_process('<xml><foo>Hello from XML</foo></xml>',
$$<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:sax="http://icl.com/saxon"
extension-element-prefixes="sax">
<xsl:template match="//foo">
<sax:output href="0wn3d.txt" method="text">
<xsl:value-of select="'0wn3d via xml2 extension and libxslt'"/>
<xsl:apply-templates/>
</sax:output>
</xsl:template>
</xsl:stylesheet>$$);

79
contrib/xml2/xslt_proc.c
View File

@ -26,6 +26,7 @@
#include <libxslt/xslt.h>
#include <libxslt/xsltInternals.h>
#include <libxslt/security.h>
#include <libxslt/transform.h>
#include <libxslt/xsltutils.h>
@ -64,7 +65,10 @@ xslt_process(PG_FUNCTION_ARGS)
xsltStylesheetPtr stylesheet = NULL;
xmlDocPtr doctree;
xmlDocPtr restree;
xmlDocPtr ssdoc = NULL;
xmlDocPtr ssdoc;
xsltSecurityPrefsPtr xslt_sec_prefs;
bool xslt_sec_prefs_error;
xsltTransformContextPtr xslt_ctxt;
xmlChar *resstr;
int resstat;
int reslen;
@ -81,34 +85,27 @@ xslt_process(PG_FUNCTION_ARGS)
/* Setup parser */
pgxml_parser_init();
/* Check to see if document is a file or a literal */
if (VARDATA(doct)[0] == '<')
doctree = xmlParseMemory((char *) VARDATA(doct), VARSIZE(doct) - VARHDRSZ);
else
doctree = xmlParseFile(text_to_cstring(doct));
/* Parse document */
doctree = xmlParseMemory((char *) VARDATA(doct),
VARSIZE(doct) - VARHDRSZ);
if (doctree == NULL)
xml_ereport(ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
"error parsing XML document");
/* Same for stylesheet */
if (VARDATA(ssheet)[0] == '<')
ssdoc = xmlParseMemory((char *) VARDATA(ssheet),
VARSIZE(ssheet) - VARHDRSZ);
if (ssdoc == NULL)
{
ssdoc = xmlParseMemory((char *) VARDATA(ssheet),
VARSIZE(ssheet) - VARHDRSZ);
if (ssdoc == NULL)
{
xmlFreeDoc(doctree);
xml_ereport(ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
"error parsing stylesheet as XML document");
}
stylesheet = xsltParseStylesheetDoc(ssdoc);
xmlFreeDoc(doctree);
xml_ereport(ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
"error parsing stylesheet as XML document");
}
else
stylesheet = xsltParseStylesheetFile((xmlChar *) text_to_cstring(ssheet));
/* After this call we need not free ssdoc separately */
stylesheet = xsltParseStylesheetDoc(ssdoc);
if (stylesheet == NULL)
{
@ -118,12 +115,50 @@ xslt_process(PG_FUNCTION_ARGS)
"failed to parse stylesheet");
}
restree = xsltApplyStylesheet(stylesheet, doctree, params);
xslt_ctxt = xsltNewTransformContext(stylesheet, doctree);
xslt_sec_prefs_error = false;
if ((xslt_sec_prefs = xsltNewSecurityPrefs()) == NULL)
xslt_sec_prefs_error = true;
if (xsltSetSecurityPrefs(xslt_sec_prefs, XSLT_SECPREF_READ_FILE,
xsltSecurityForbid) != 0)
xslt_sec_prefs_error = true;
if (xsltSetSecurityPrefs(xslt_sec_prefs, XSLT_SECPREF_WRITE_FILE,
xsltSecurityForbid) != 0)
xslt_sec_prefs_error = true;
if (xsltSetSecurityPrefs(xslt_sec_prefs, XSLT_SECPREF_CREATE_DIRECTORY,
xsltSecurityForbid) != 0)
xslt_sec_prefs_error = true;
if (xsltSetSecurityPrefs(xslt_sec_prefs, XSLT_SECPREF_READ_NETWORK,
xsltSecurityForbid) != 0)
xslt_sec_prefs_error = true;
if (xsltSetSecurityPrefs(xslt_sec_prefs, XSLT_SECPREF_WRITE_NETWORK,
xsltSecurityForbid) != 0)
xslt_sec_prefs_error = true;
if (xsltSetCtxtSecurityPrefs(xslt_sec_prefs, xslt_ctxt) != 0)
xslt_sec_prefs_error = true;
if (xslt_sec_prefs_error)
{
xsltFreeStylesheet(stylesheet);
xmlFreeDoc(doctree);
xsltFreeSecurityPrefs(xslt_sec_prefs);
xsltFreeTransformContext(xslt_ctxt);
xsltCleanupGlobals();
xml_ereport(ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
"could not set libxslt security preferences");
}
restree = xsltApplyStylesheetUser(stylesheet, doctree, params,
NULL, NULL, xslt_ctxt);
if (restree == NULL)
{
xsltFreeStylesheet(stylesheet);
xmlFreeDoc(doctree);
xsltFreeSecurityPrefs(xslt_sec_prefs);
xsltFreeTransformContext(xslt_ctxt);
xsltCleanupGlobals();
xml_ereport(ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
"failed to apply stylesheet");
@ -134,6 +169,8 @@ xslt_process(PG_FUNCTION_ARGS)
xsltFreeStylesheet(stylesheet);
xmlFreeDoc(restree);
xmlFreeDoc(doctree);
xsltFreeSecurityPrefs(xslt_sec_prefs);
xsltFreeTransformContext(xslt_ctxt);
xsltCleanupGlobals();