HTTP header injection vulnerabilities arise when user-supplied data is copied into a response header in an unsafe way. If an attacker can inject newline characters into the header, then they can inject new HTTP headers and also, by injecting an empty line, break out of the headers into the message body and write arbitrary content into the application's response.
Various kinds of attack can be delivered via HTTP header injection vulnerabilities. Any attack that can be delivered via cross-site scripting can usually be delivered via header injection, because the attacker can construct a request which causes arbitrary JavaScript to appear within the response body. Further, it is sometimes possible to leverage header injection vulnerabilities to poison the cache of any proxy server via which users access the application. Here, an attacker sends a crafted request which results in a "split" response containing arbitrary content. If the proxy server can be manipulated to associate the injected response with another URL used within the application, then the attacker can perform a "stored" attack against this URL which will compromise other users who request that URL in future.
Issue remediation
If possible, applications should avoid copying user-controllable data into HTTP response headers. If this is unavoidable, then the data should be strictly validated to prevent header injection attacks. In most situations, it will be appropriate to allow only short alphanumeric strings to be copied into headers, and any other input should be rejected. At a minimum, input containing any characters with ASCII codes less than 0x20 should be rejected.
The value of the ADCUserID cookie is copied into the Set-cookie response header. The payload c222f%0d%0a5c335e93809 was submitted in the ADCUserID cookie. This caused a response containing an injected HTTP header.
Request
GET /adcentric/click/1728/2/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=c222f%0d%0a5c335e93809; 1728-1-50458=12300;
The value of the ADCUserID cookie is copied into the Set-cookie response header. The payload dddf0%0d%0ae1f4a682539 was submitted in the ADCUserID cookie. This caused a response containing an injected HTTP header.
Request
GET /adcentric/data/1728/1/50458;image\ HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=dddf0%0d%0ae1f4a682539; 1728-1-50458=12300;
The value of the ADCUserID cookie is copied into the Set-cookie response header. The payload 94add%0d%0a21c43d4d130 was submitted in the ADCUserID cookie. This caused a response containing an injected HTTP header.
Request
GET /adcentric/event/1728/3/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=94add%0d%0a21c43d4d130; 1728-1-50458=12300;
The value of the ADCUserID cookie is copied into the Set-cookie response header. The payload d9cae%0d%0ab69c9c46b1 was submitted in the ADCUserID cookie. This caused a response containing an injected HTTP header.
Request
GET /adcentric/form/1728/2/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=d9cae%0d%0ab69c9c46b1; 1728-1-50458=12300;
The value of the ADCUserID cookie is copied into the Set-cookie response header. The payload 82e3e%0d%0aaee656c8f57 was submitted in the ADCUserID cookie. This caused a response containing an injected HTTP header.
Request
GET /adcentric/tag/1728/1/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=82e3e%0d%0aaee656c8f57; 1728-1-50458=12300;
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 edee1"><script>alert(1)</script>8e08934f7a4 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.
Issue background
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 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.
Request
GET /adcentric/form/1728/2/50458?edee1"><script>alert(1)</script>8e08934f7a4=1 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
The application publishes a Flash cross-domain policy which allows access from any domain.
Allowing access from all domains means that any domain can perform two-way interaction with this application. Unless the application consists entirely of unprotected public content, this policy is likely to present a significant security risk.
Issue background
The Flash cross-domain policy controls whether Flash client components running on other domains can perform two-way interaction with the domain which publishes the policy. If another domain is allowed by the policy, then that domain can potentially attack users of the application. If a user is logged in to the application, and visits a domain allowed by the policy, then any malicious content running on that domain can potentially gain full access to the application within the security context of the logged in user.
Even if an allowed domain is not overtly malicious in itself, security vulnerabilities within that domain could potentially be leveraged by a third-party attacker to exploit the trust relationship and attack the application which allows access.
Issue remediation
You should review the domains which are allowed by the Flash cross-domain policy and determine whether it is appropriate for the application to fully trust both the intentions and security posture of those domains.
Request
GET /crossdomain.xml HTTP/1.0 Host: assets.adcentriconline.com
Response
HTTP/1.1 200 OK Server: nginx/0.7.65 Date: Sat, 20 Nov 2010 08:07:55 GMT Content-Type: text/xml Content-Length: 100 Last-Modified: Thu, 14 Jan 2010 22:08:54 GMT Connection: close P3P: CP="NOI OTC OTP OUR NOR" X-RealServer: h010 Accept-Ranges: bytes
A cookie's domain attribute determines which domains can access the cookie. Browsers will automatically submit the cookie in requests to in-scope domains, and those domains will also be able to access the cookie via JavaScript. If a cookie is scoped to a parent domain, then that cookie will be accessible by the parent domain and also by any other subdomains of the parent domain. If the cookie contains sensitive data (such as a session token) then this data may be accessible by less trusted or less secure applications residing at those domains, leading to a security compromise.
Issue remediation
By default, cookies are scoped to the issuing domain and all subdomains. If you remove the explicit domain attribute from your Set-cookie directive, then the cookie will have this default scope, which is safe and appropriate in most situations. If you particularly need a cookie to be accessible by a parent domain, then you should thoroughly review the security of the applications residing on that domain and its subdomains, and confirm that you are willing to trust the people and systems which support those applications.
The cookie does not appear to contain a session token, which may reduce the risk associated with this issue. You should review the contents of the cookie to determine its function.
Request
GET /adcentric/click/1728/2/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
The cookies do not appear to contain session tokens, which may reduce the risk associated with this issue. You should review the contents of the cookies to determine their function.
Request
GET /adcentric/data/1728/1/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
The cookie does not appear to contain a session token, which may reduce the risk associated with this issue. You should review the contents of the cookie to determine its function.
Request
GET /adcentric/event/1728/3/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
The cookie does not appear to contain a session token, which may reduce the risk associated with this issue. You should review the contents of the cookie to determine its function.
Request
GET /adcentric/form/1728/2/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
The cookies do not appear to contain session tokens, which may reduce the risk associated with this issue. You should review the contents of the cookies to determine their function.
Request
GET /adcentric/tag/1728/1/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
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.
The cookie does not appear to contain a session token, which may reduce the risk associated with this issue. You should review the contents of the cookie to determine its function.
Request
GET /adcentric/click/1728/2/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
The cookies do not appear to contain session tokens, which may reduce the risk associated with this issue. You should review the contents of the cookies to determine their function.
Request
GET /adcentric/data/1728/1/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
The cookie does not appear to contain a session token, which may reduce the risk associated with this issue. You should review the contents of the cookie to determine its function.
Request
GET /adcentric/event/1728/3/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
The cookie does not appear to contain a session token, which may reduce the risk associated with this issue. You should review the contents of the cookie to determine its function.
Request
GET /adcentric/form/1728/2/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
The cookies do not appear to contain session tokens, which may reduce the risk associated with this issue. You should review the contents of the cookies to determine their function.
Request
GET /adcentric/tag/1728/1/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
If a web response states that it contains HTML content but does not specify a character set, 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.
GET /adcentric/click/1728/2/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
GET /adcentric/data/1728/1/50458;image\ HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
GET /adcentric/event/1728/3/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;
GET /adcentric/form/1728/2/50458 HTTP/1.1 Host: adc2.adcentriconline.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: ADCUserID=NkDrm5M4SVIi4zZ; 1728-1-50458=12300;