SQL injection vulnerabilities arise when user-controllable data is incorporated into database SQL queries in an unsafe manner. An attacker can supply crafted input to break out of the data context in which their input appears and interfere with the structure of the surrounding query.
Various attacks can be delivered via SQL injection, including reading or modifying critical application data, interfering with application logic, escalating privileges within the database and executing operating system commands.
Remediation background
The most effective way to prevent SQL injection attacks is to use parameterised queries (also known as prepared statements) for all database access. This method uses two steps to incorporate potentially tainted data into SQL queries: first, the application specifies the structure of the query, leaving placeholders for each item of user input; second, the application specifies the contents of each placeholder. Because the structure of the query has already defined in the first step, it is not possible for malformed data in the second step to interfere with the query structure. You should review the documentation for your database and application platform to determine the appropriate APIs which you can use to perform parameterised queries. It is strongly recommended that you parameterise every variable data item that is incorporated into database queries, even if it is not obviously tainted, to prevent oversights occurring and avoid vulnerabilities being introduced by changes elsewhere within the code base of the application.
You should be aware that some commonly employed and recommended mitigations for SQL injection vulnerabilities are not always effective:
One common defence is to double up any single quotation marks appearing within user input before incorporating that input into a SQL query. This defence is designed to prevent malformed data from terminating the string in which it is inserted. However, if the data being incorporated into queries is numeric, then the defence may fail, because numeric data may not be encapsulated within quotes, in which case only a space is required to break out of the data context and interfere with the query. Further, in second-order SQL injection attacks, data that has been safely escaped when initially inserted into the database is subsequently read from the database and then passed back to it again. Quotation marks that have been doubled up initially will return to their original form when the data is reused, allowing the defence to be bypassed.
Another often cited defence is to use stored procedures for database access. While stored procedures can provide security benefits, they are not guaranteed to prevent SQL injection attacks. The same kinds of vulnerabilities that arise within standard dynamic SQL queries can arise if any SQL is dynamically constructed within stored procedures. Further, even if the procedure is sound, SQL injection can arise if the procedure is invoked in an unsafe manner using user-controllable data.
The productid parameter appears to be vulnerable to SQL injection attacks. The payload ' was submitted in the productid parameter, and a database error message was returned. You should review the contents of the error message, and the application's handling of other input, to confirm whether a vulnerability is present.
The database appears to be MySQL.
Remediation detail
The application should handle errors gracefully and prevent SQL error messages from being returned in responses.
<p>Severity: Notice</p> <p>Message: Undefined index: 1011956760'</p> <p>Filename: mo ...[SNIP]... ctdescriptions pd2 ON (p.productid = pd2.productid AND pd2.type = '3' AND pd2.localeid = '3') JOIN manufacturer m ON (p.manufacturerid = m.manufacturerid) WHERE p.productid = '1011956760'' 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 ''1011956760''' at line 7
The REST URL parameter 3 appears to be vulnerable to SQL injection attacks. The payload ' was submitted in the REST URL parameter 3, and a database error message was returned. You should review the contents of the error message, and the application's handling of other input, to confirm whether a vulnerability is present.
The database appears to be MySQL.
Remediation detail
The application should handle errors gracefully and prevent SQL error messages from being returned in responses.
Request
GET /products/details/McAfee-SafeBoot-Web-Server-SSL-Certificate-with-1-Year-Gold-Support-1-User-1011956760'?utm_source=google&utm_medium=product-search HTTP/1.1 Host: www.microcad.ca Proxy-Connection: keep-alive Referer: http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=ssl+certificates#q=ssl+certificates&hl=en&prmd=ivnsufd&source=lnms&tbm=shop&ei=_5tiTr_COO_SiAKums2VCg&sa=X&oi=mode_link&ct=mode&cd=5&ved=0CFYQ_AUoBA&bav=on.2,or.r_gc.r_pw.&fp=d8e70e66cd7c7a51&biw=1233&bih=1037 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.218 Safari/535.1 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 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
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 '\' AND an.localeid = '3' AND hn.localeid = '3' AND pa.localeid = '3' ORDE' at line 7
The value of the productid request parameter submitted to the URL /cart/add/ is copied into the value of an HTML tag attribute which is encapsulated in single quotation marks at the URL /cart. The payload 1542d'><script>alert(1)</script>91926b477ff was submitted in the productid parameter. This input was returned unmodified in a subsequent request for the URL /cart.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Issue background
Stored cross-site scripting vulnerabilities arise when data which originated from any tainted source is copied into the application's responses in an unsafe way. An attacker can use the vulnerability to inject malicious JavaScript code into the application, which will execute within the browser of any user who views the relevant application content.
The attacker-supplied code can perform a wide variety of actions, such as stealing victims' session tokens or login credentials, performing arbitrary actions on their behalf, and logging their keystrokes.
Methods for introducing malicious content include any function where request parameters or headers are processed and stored by the application, and any out-of-band channel whereby data can be introduced into the application's processing space (for example, email messages sent over SMTP which are ultimately rendered within a web mail application).
Stored cross-site scripting flaws are typically more serious than reflected vulnerabilities because they do not require a separate delivery mechanism in order to reach target users, and they can potentially be exploited to create web application worms which spread exponentially amongst application users.
Note that automated detection of stored cross-site scripting vulnerabilities cannot reliably determine whether attacks that are persisted within the application can be accessed by any other user, only by authenticated users, or only by the attacker themselves. You should review the functionality in which the vulnerability appears to determine whether the application's behaviour can feasibly be used to compromise other application users.
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 productid request parameter is copied into the value of an HTML tag attribute which is encapsulated in single quotation marks. The payload 36039%2527%253e%253cscript%253ealert%25281%2529%253c%252fscript%253e6607268138f was submitted in the productid parameter. This input was echoed as 36039'><script>alert(1)</script>6607268138f 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.
Note that a redirection occurred between the attack request and the response containing the echoed input. It is necessary to follow this redirection for the attack to succeed. When the attack is carried out via a browser, the redirection will be followed automatically.
Remediation detail
There is probably no need to perform a second URL-decode of the value of the productid request parameter 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.
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.
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 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.
When a web browser makes a request for a resource, it typically adds an HTTP header, called the "Referer" header, indicating the URL of the resource from which the request originated. This occurs in numerous situations, for example when a web page loads an image or script, or when a user clicks on a link or submits a form.
If the resource being requested resides on a different domain, then the Referer header is still generally included in the cross-domain request. If the originating URL contains any sensitive information within its query string, such as a session token, then this information will be transmitted to the other domain. If the other domain is not fully trusted by the application, then this may lead to a security compromise.
You should review the contents of the information being transmitted to other domains, and also determine whether those domains are fully trusted by the originating application.
Today's browsers may withhold the Referer header in some situations (for example, when loading a non-HTTPS resource from a page that was loaded over HTTPS, or when a Refresh directive is issued), but this behaviour should not be relied upon to protect the originating URL from disclosure.
Note also that if users can author content within the application then an attacker may be able to inject links referring to a domain they control in order to capture data from URLs used within the application.
Issue remediation
The application should never transmit any sensitive information within the URL query string. In addition to being leaked in the Referer header, such information may be logged in various locations and may be visible on-screen to untrusted parties.
Request
GET /products/details/McAfee-SafeBoot-Web-Server-SSL-Certificate-with-1-Year-Gold-Support-1-User-1011956760?utm_source=google&utm_medium=product-search HTTP/1.1 Host: www.microcad.ca Proxy-Connection: keep-alive Referer: http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=ssl+certificates#q=ssl+certificates&hl=en&prmd=ivnsufd&source=lnms&tbm=shop&ei=_5tiTr_COO_SiAKums2VCg&sa=X&oi=mode_link&ct=mode&cd=5&ved=0CFYQ_AUoBA&bav=on.2,or.r_gc.r_pw.&fp=d8e70e66cd7c7a51&biw=1233&bih=1037 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.218 Safari/535.1 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 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
When an application includes a script from an external domain, this script is executed by the browser within the security context of the invoking application. The script can therefore do anything that the application's own scripts can do, such as accessing application data and performing actions within the context of the current user.
If you include a script from an external domain, then you are trusting that domain with the data and functionality of your application, and you are trusting the domain's own security to prevent an attacker from modifying the script to perform malicious actions within your application.
Issue remediation
Scripts should not be included from untrusted domains. If you have a requirement which a third-party script appears to fulfil, then you should ideally copy the contents of that script onto your own domain and include it from there. If that is not possible (e.g. for licensing reasons) then you should consider reimplementing the script's functionality within your own code.
The file robots.txt is used to give instructions to web robots, such as search engine crawlers, about locations within the web site which robots are allowed, or not allowed, to crawl and index.
The presence of the robots.txt does not in itself present any kind of security vulnerability. However, it is often used to identify restricted or private areas of a site's contents. The information in the file may therefore help an attacker to map out the site's contents, especially if some of the locations identified are not linked from elsewhere in the site. If the application relies on robots.txt to protect access to these areas, and does not enforce proper access control over them, then this presents a serious vulnerability.
Issue remediation
The robots.txt file is not itself a security threat, and its correct use can represent good practice for non-security reasons. You should not assume that all web robots will honour the file's instructions. Rather, assume that attackers will pay close attention to any locations identified in the file. Do not rely on robots.txt to provide any kind of protection over unauthorised access.
The response contains the following Content-type statement:
Content-Type: image/gif
The response states that it contains a GIF image. However, it actually appears to contain a PNG image.
Issue background
If a web response specifies an incorrect content type, then browsers may process the response in unexpected ways. If the specified content type is a renderable text-based format, then the browser will usually attempt to parse and render the response in that format. If the specified type is an image format, then the browser will usually detect the anomaly and will analyse the actual content and attempt to determine its MIME type. Either case can lead to unexpected results, and if the content contains any user-controllable data may lead to cross-site scripting or other client-side vulnerabilities.
In most cases, the presence of an incorrect content type statement 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 a message body, the application should include a single Content-type header which correctly and unambiguously states the MIME type of the content in the response body.
