XPath Injection

Constructing a dynamic XPath query with user input may allow an attacker to modify the statement's meaning.

XPath injection occurs when:

1. Data enters a program from an untrusted source.



2. The data used to dynamically construct an XPath query.

Example 1: The following code dynamically constructs and executes an XPath query that retrieves an email address for a given account ID. The account ID is read from an HTTP request, and is therefore untrusted.

...
string acctID = Request["acctID"];
string query = null;
if(acctID != null) {
       StringBuffer sb = new StringBuffer("/accounts/account[acctID='");
       sb.append(acctID);
       sb.append("']/email/text()");
       query = sb.toString();
}

XPathDocument docNav = new XPathDocument(myXml);
XPathNavigator nav = docNav.CreateNavigator();
nav.Evaluate(query);
...

Under normal conditions, such as searching for an email address that belongs to the account number 1, the query that this code executes will look like the following:

/accounts/account[acctID='1']/email/text()

However, because the query is constructed dynamically by concatenating a constant base query string and a user input string, the query only behaves correctly if acctID does not contain a single-quote character. If an attacker enters the string 1' or '1' = '1 for acctID, then the query becomes the following:

/accounts/account[acctID='1' or '1' = '1']/email/text()

The addition of the 1' or '1' = '1 condition causes the where clause to always evaluate to true, so the query becomes logically equivalent to the much simpler query:

//email/text()

This simplification of the query allows the attacker to bypass the requirement that the query must only return items owned by the authenticated user. The query now returns all email addresses stored in the document, regardless of their specified owner.

The identified method invokes an XPath query built using unvalidated input. This call could allow an attacker to modify the statement's meaning or to execute arbitrary XPath queries.

XPath injection occurs when:

1. Data enters a program from an untrusted source.




2. The data used to dynamically construct an XPath query.

Example 1: The following Objective-C code, which calls C APIs, dynamically constructs and executes an XPath query that retrieves an email address for a given account ID. The account ID is read from an HTTP request, and is therefore untrusted.

...
    NSString *accountStr = account.text;

    xmlXPathContextPtr xpathCtx;
    NSString *query = @"/accounts/account[actId='" + accountStr + @"']/email/text()";

    xpathCtx = xmlXPathNewContext(doc);

    /* Evaluate XPath expression */
    xmlChar *queryString =
        (xmlChar *)[query cStringUsingEncoding:NSUTF8StringEncoding];
    xpathObj = xmlXPathEvalExpression(queryString, xpathCtx);
...

Under normal conditions, such as searching for an email address that belongs to the account number 1, the query that this code executes will look like the following:

/accounts/account[acctID='1']/email/text()

However, because the query is constructed dynamically by concatenating a constant base query string and a user input string, the query only behaves correctly if acctID does not contain a single-quote character. If an attacker enters the string 1' or '1' = '1 for acctID, then the query becomes the following:

/accounts/account[acctID='1' or '1' = '1']/email/text()

The addition of the 1' or '1' = '1 condition causes the where clause to always evaluate to true, so the query becomes logically equivalent to the much simpler query:

//email/text()

This simplification of the query allows the attacker to bypass the requirement that the query must only return items owned by the authenticated user. The query now returns all email addresses stored in the document, regardless of their specified owner.

Constructing a dynamic XPath query with user input could allow an attacker to modify the statement's meaning.

XPath injection occurs when:

1. Data enters a program from an untrusted source.



2. The data used to dynamically construct an XPath query.

Example 1: The following code dynamically constructs and executes an XPath query that retrieves an email address for a given account ID. The account ID is read from an HTTP request, and is therefore untrusted.

query = "/accounts/account[acctID='" & url.acctID & "']/email/text()";
selectedElements = XmlSearch(myxmldoc, query);

Under normal conditions, such as searching for an email address that belongs to the account number 1, the query that this code executes will look like the following:

/accounts/account[acctID='1']/email/text()

However, because the query is constructed dynamically by concatenating a constant base query string and a user input string, the query only behaves correctly if acctID does not contain a single-quote character. If an attacker enters the string 1' or '1' = '1 for acctID, then the query becomes the following:

/accounts/account[acctID='1' or '1' = '1']/email/text()

The addition of the 1' or '1' = '1 condition causes the where clause to always evaluate to true, so the query becomes logically equivalent to the much simpler query:

//email/text()

This simplification of the query allows the attacker to bypass the requirement that the query must only return items owned by the authenticated user. The query now returns all email addresses stored in the document, regardless of their specified owner.

The identified method invokes an XPath query built using unvalidated input. This call could allow an attacker to modify the statement's meaning or to execute arbitrary XPath queries.

XPath injection occurs when:

1. Data enters a program from an untrusted source.




2. The data used to dynamically construct an XPath query.

Example 1: The following code dynamically constructs and executes an XPath query that retrieves an email address for a given account ID. The account ID is read from an HTTP request, and is therefore untrusted.

...
    NSString *accountStr = account.text;

    xmlXPathContextPtr xpathCtx;
    NSString *query = @"/accounts/account[actId='" + accountStr + @"']/email/text()";

    xpathCtx = xmlXPathNewContext(doc);

    /* Evaluate XPath expression */
    xmlChar *queryString =
        (xmlChar *)[query cStringUsingEncoding:NSUTF8StringEncoding];
    xpathObj = xmlXPathEvalExpression(queryString, xpathCtx);
...

Under normal conditions, such as searching for an email address that belongs to the account number 1, the query that this code executes will look like the following:

/accounts/account[acctID='1']/email/text()

However, because the query is constructed dynamically by concatenating a constant base query string and a user input string, the query only behaves correctly if acctID does not contain a single-quote character. If an attacker enters the string 1' or '1' = '1 for acctID, then the query becomes the following:

/accounts/account[acctID='1' or '1' = '1']/email/text()

The addition of the 1' or '1' = '1 condition causes the where clause to always evaluate to true, so the query becomes logically equivalent to the much simpler query:

//email/text()

This simplification of the query allows the attacker to bypass the requirement that the query must only return items owned by the authenticated user. The query now returns all email addresses stored in the document, regardless of their specified owner.

Constructing a dynamic XPath query with user input could allow an attacker to modify the statement's meaning.

XPath injection occurs when:

1. Data enters a program from an untrusted source.



2. The data is used to dynamically construct an XPath query.

Example 1: The following code dynamically constructs and executes an XPath query that retrieves an email address for a given account ID. The account ID is read from an HTTP request, and is therefore untrusted.

...
<?php
load('articles.xml');

$xpath = new DOMXPath($doc);
$emailAddrs = $xpath->query("/accounts/account[acctID='" . $_GET["test1"] . "']/email/text()");
//$arts = $xpath->evaluate("/accounts/account[acctID='" . $_GET["test1"] . "']/email/text()")

foreach ($emailAddrs as $email)
{
    echo $email->nodeValue."";
}
	?>
...

Under normal conditions, such as searching for an email address that belongs to the account number 1, the query that this code executes will look like the following:

/accounts/account[acctID='1']/email/text()

However, because the query is constructed dynamically by concatenating a constant query string and a user input string, the query only behaves correctly if acctID does not contain a single-quote character. If an attacker enters the string 1' or '1' = '1 for acctID, then the query becomes the following:

/accounts/account[acctID='1' or '1' = '1']/email/text()

The addition of the 1' or '1' = '1 condition causes the where clause to always evaluate to true, so the query becomes logically equivalent to the much simpler query:

//email/text()

This simplification of the query allows the attacker to bypass the requirement that the query must only return items owned by the authenticated user. The query now returns all email addresses stored in the document, regardless of their specified owner.

Constructing a dynamic XPath query with user input could allow an attacker to modify the statement's meaning.

XPath injection occurs when:

1. Data enters a program from an untrusted source.



2. The data is used to dynamically construct an XPath query.

Example 1: The following code dynamically constructs and executes an XPath query that retrieves an email address for a given account ID. The account ID is read from an HTTP request, and is therefore untrusted.

...
tree = etree.parse('articles.xml')
emailAddrs = "/accounts/account[acctID=" + request.GET["test1"] + "]/email/text()"
r = tree.xpath(emailAddrs)
...

Under normal conditions, such as searching for an email address that belongs to the account number 1, the query that this code executes will look like the following:

/accounts/account[acctID='1']/email/text()

However, because the query is constructed dynamically by concatenating a constant query string and a user input string, the query only behaves correctly if acctID does not contain a single-quote character. If an attacker enters the string 1' or '1' = '1 for acctID, then the query becomes the following:

/accounts/account[acctID='1' or '1' = '1']/email/text()

The addition of the 1' or '1' = '1 condition causes the where clause to always evaluate to true, so the query becomes logically equivalent to the much simpler query:

//email/text()

This simplification of the query allows the attacker to bypass the requirement that the query must only return items owned by the authenticated user. The query now returns all email addresses stored in the document, regardless of their specified owner.