[Forgot Password]
Login  Register Subscribe












Paid content will be excluded from the download.

Download | Alert*
view XML

Improper Neutralization of Script in an Error Message Web Page

ID: 81Date: (C)2012-05-14   (M)2012-11-08
Type: weaknessStatus: INCOMPLETE
Abstraction Type: Variant


The software receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters that could be interpreted as web-scripting elements when they are sent to an error page.

Extended Description

Error pages may include customized 403 Forbidden or 404 Not Found pages.

When an attacker can trigger an error that contains unneutralized input, then cross-site scripting attacks may be possible.

Applicable Platforms
Language Class: All

Time Of Introduction

  • Implementation
  • Operation

Related Attack Patterns

Common Consequences

ScopeTechnical ImpactNotes
Read application data
Execute unauthorized code or commands

Detection Methods

Potential Mitigations

  Do not write user-controlled input to error pages.
 Carefully check each input parameter against a rigorous positive specification (white list) defining the specific characters and format allowed. All input should be neutralized, not just parameters that the user is supposed to specify, but all data in the request, including hidden fields, cookies, headers, the URL itself, and so forth. A common mistake that leads to continuing XSS vulnerabilities is to validate only fields that are expected to be redisplayed by the site. We often encounter data from the request that is reflected by the application server or the application that the development team did not anticipate. Also, a field that is not currently reflected may be used by a future developer. Therefore, validating ALL parts of the HTTP request is recommended.
Output Encoding
Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component.
The problem of inconsistent output encodings often arises in web pages. If an encoding is not specified in an HTTP header, web browsers often guess about which encoding is being used. This can open up the browser to subtle XSS attacks.
 With Struts, write all data from form beans with the bean's filter attribute set to true.
Identify and Reduce Attack Surface
To help mitigate XSS attacks against the user's session cookie, set the session cookie to be HttpOnly. In browsers that support the HttpOnly feature (such as more recent versions of Internet Explorer and Firefox), this attribute can prevent the user's session cookie from being accessible to malicious client-side scripts that use document.cookie. This is not a complete solution, since HttpOnly is not supported by all browsers. More importantly, XMLHTTPRequest and other powerful browser technologies provide read access to HTTP headers, including the Set-Cookie header in which the HttpOnly flag is set.
Defense in Depth


Related CWETypeViewChain
CWE-81 ChildOf CWE-896 Category CWE-888  

Demonstrative Examples

Observed Examples

  1. CVE-2002-0840 : XSS in default error page from Host: header.
  2. CVE-2002-1053 : XSS in error message.
  3. CVE-2002-1700 : XSS in error page from targeted parameter.

For more examples, refer to CVE relations in the bottom box.

White Box Definitions

Black Box Definitions

Taxynomy Mappings

PLOVER  XSS in error pages


  1. Michael Howard David LeBlanc John Viega .24 Deadly Sins of Software Security. McGraw-Hill. Section:'"Sin 11: Failure to Handle Errors Correctly." Page 183'. Published on 2010.

© 2013 SecPod Technologies