Common Weakness Enumeration

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CWE-209: Information Exposure Through an Error Message

Weakness ID: 209
Abstraction: Base
Status: Draft
Presentation Filter:
+ Description

Description Summary

The software generates an error message that includes sensitive information about its environment, users, or associated data.

Extended Description

The sensitive information may be valuable information on its own (such as a password), or it may be useful for launching other, more deadly attacks. If an attack fails, an attacker may use error information provided by the server to launch another more focused attack. For example, an attempt to exploit a path traversal weakness (CWE-22) might yield the full pathname of the installed application. In turn, this could be used to select the proper number of ".." sequences to navigate to the targeted file. An attack using SQL injection (CWE-89) might not initially succeed, but an error message could reveal the malformed query, which would expose query logic and possibly even passwords or other sensitive information used within the query.

+ Time of Introduction
  • Architecture and Design
  • Implementation
  • System Configuration
  • Operation
+ Applicable Platforms


PHP: (Often)


+ Common Consequences

Technical Impact: Read application data

Often this will either reveal sensitive information which may be used for a later attack or private information stored in the server.

+ Likelihood of Exploit


+ Detection Methods

Manual Analysis

This weakness generally requires domain-specific interpretation using manual analysis. However, the number of potential error conditions may be too large to cover completely within limited time constraints.

Effectiveness: High

Automated Analysis

Automated methods may be able to detect certain idioms automatically, such as exposed stack traces or pathnames, but violation of business rules or privacy requirements is not typically feasible.

Effectiveness: Moderate

Automated Dynamic Analysis

This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Error conditions may be triggered with a stress-test by calling the software simultaneously from a large number of threads or processes, and look for evidence of any unexpected behavior.

Effectiveness: Moderate

Manual Dynamic Analysis

Identify error conditions that are not likely to occur during normal usage and trigger them. For example, run the program under low memory conditions, run with insufficient privileges or permissions, interrupt a transaction before it is completed, or disable connectivity to basic network services such as DNS. Monitor the software for any unexpected behavior. If you trigger an unhandled exception or similar error that was discovered and handled by the application's environment, it may still indicate unexpected conditions that were not handled by the application itself.

+ Demonstrative Examples

Example 1

In the following example, sensitive information might be printed depending on the exception that occurs.

(Bad Code)
Example Language: Java 
try {
catch (Exception e) {

If an exception related to SQL is handled by the catch, then the output might contain sensitive information such as SQL query structure or private information. If this output is redirected to a web user, this may represent a security problem.

Example 2

This code tries to open a database connection, and prints any exceptions that occur.

(Bad Code)
Example Language: PHP 
try {
//print exception message that includes exception message and configuration file location
catch (Exception $e) {
echo 'Caught exception: ', $e->getMessage(), '\n';
echo 'Check credentials in config file at: ', $Mysql_config_location, '\n';

If an exception occurs, the printed message exposes the location of the configuration file the script is using. An attacker can use this information to target the configuration file (perhaps exploiting a Path Traversal weakness). If the file can be read, the attacker could gain credentials for accessing the database. The attacker may also be able to replace the file with a malicious one, causing the application to use an arbitrary database.

Example 3

The following code generates an error message that leaks the full pathname of the configuration file.

(Bad Code)
Example Language: Perl 
$ConfigDir = "/home/myprog/config";
$uname = GetUserInput("username");
# avoid CWE-22, CWE-78, others.
ExitError("Bad hacker!") if ($uname !~ /^\w+$/);
$file = "$ConfigDir/$uname.txt";
if (! (-e $file)) {
ExitError("Error: $file does not exist");

If this code is running on a server, such as a web application, then the person making the request should not know what the full pathname of the configuration directory is. By submitting a username that does not produce a $file that exists, an attacker could get this pathname. It could then be used to exploit path traversal or symbolic link following problems that may exist elsewhere in the application.

Example 4

In the example below, the method getUserBankAccount retrieves a bank account object from a database using the supplied username and account number to query the database. If an SQLException is raised when querying the database, an error message is created and output to a log file.

(Bad Code)
Example Language: Java 
public BankAccount getUserBankAccount(String username, String accountNumber) {
BankAccount userAccount = null;
String query = null;
try {
if (isAuthorizedUser(username)) {
query = "SELECT * FROM accounts WHERE owner = "
+ username + " AND accountID = " + accountNumber;
DatabaseManager dbManager = new DatabaseManager();
Connection conn = dbManager.getConnection();
Statement stmt = conn.createStatement();
ResultSet queryResult = stmt.executeQuery(query);
userAccount = (BankAccount)queryResult.getObject(accountNumber);
} catch (SQLException ex) {
String logMessage = "Unable to retrieve account information from database,\nquery: " + query;
Logger.getLogger(BankManager.class.getName()).log(Level.SEVERE, logMessage, ex);
return userAccount;

The error message that is created includes information about the database query that may contain sensitive information about the database or query logic. In this case, the error message will expose the table name and column names used in the database. This data could be used to simplify other attacks, such as SQL injection (CWE-89) to directly access the database.

+ Observed Examples
POP3 server reveals a password in an error message after multiple APOP commands are sent. Might be resultant from another weakness.
Program reveals password in error message if attacker can trigger certain database errors.
Composite: application running with high privileges allows user to specify a restricted file to process, which generates a parsing error that leaks the contents of the file.
Existence of user names can be determined by requesting a nonexistent blog and reading the error message.
Direct request to library file in web application triggers pathname leak in error message.
Malformed input to login page causes leak of full path when IMAP call fails.
Malformed regexp syntax leads to information exposure in error message.
+ Potential Mitigations

Phase: Implementation

Ensure that error messages only contain minimal details that are useful to the intended audience, and nobody else. The messages need to strike the balance between being too cryptic and not being cryptic enough. They should not necessarily reveal the methods that were used to determine the error. Such detailed information can be used to refine the original attack to increase the chances of success.

If errors must be tracked in some detail, capture them in log messages - but consider what could occur if the log messages can be viewed by attackers. Avoid recording highly sensitive information such as passwords in any form. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a username is valid or not.

Phase: Implementation

Handle exceptions internally and do not display errors containing potentially sensitive information to a user.

Phase: Implementation

Strategy: Identify and Reduce Attack Surface

Use naming conventions and strong types to make it easier to spot when sensitive data is being used. When creating structures, objects, or other complex entities, separate the sensitive and non-sensitive data as much as possible.

Effectiveness: Defense in Depth

This makes it easier to spot places in the code where data is being used that is unencrypted.

Phases: Implementation; Build and Compilation

Strategies: Compilation or Build Hardening; Environment Hardening

Debugging information should not make its way into a production release.

Phase: System Configuration

Where available, configure the environment to use less verbose error messages. For example, in PHP, disable the display_errors setting during configuration, or at runtime using the error_reporting() function.

Phase: System Configuration

Create default error pages or messages that do not leak any information.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class200Information Exposure
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfCategoryCategory717OWASP Top Ten 2007 Category A6 - Information Leakage and Improper Error Handling
Weaknesses in OWASP Top Ten (2007) (primary)629
ChildOfCategoryCategory728OWASP Top Ten 2004 Category A7 - Improper Error Handling
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory731OWASP Top Ten 2004 Category A10 - Insecure Configuration Management
Weaknesses in OWASP Top Ten (2004)711
ChildOfCategoryCategory7512009 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2009 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)750
ChildOfWeakness ClassWeakness Class755Improper Handling of Exceptional Conditions
Research Concepts1000
ChildOfCategoryCategory8012010 Top 25 - Insecure Interaction Between Components
Weaknesses in the 2010 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)800
ChildOfCategoryCategory815OWASP Top Ten 2010 Category A6 - Security Misconfiguration
Weaknesses in OWASP Top Ten (2010) (primary)809
ChildOfCategoryCategory851CERT Java Secure Coding Section 06 - Exceptional Behavior (ERR)
Weaknesses Addressed by the CERT Java Secure Coding Standard (primary)844
ChildOfCategoryCategory8672011 Top 25 - Weaknesses On the Cusp
Weaknesses in the 2011 CWE/SANS Top 25 Most Dangerous Software Errors (primary)900
ChildOfCategoryCategory880CERT C++ Secure Coding Section 12 - Exceptions and Error Handling (ERR)
Weaknesses Addressed by the CERT C++ Secure Coding Standard (primary)868
ChildOfCategoryCategory933OWASP Top Ten 2013 Category A5 - Security Misconfiguration
Weaknesses in OWASP Top Ten (2013) (primary)928
ChildOfCategoryCategory963SFP Secondary Cluster: Exposed Data
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness BaseWeakness Base210Information Exposure Through Self-generated Error Message
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base211Information Exposure Through Externally-generated Error Message
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant550Information Exposure Through Server Error Message
Development Concepts (primary)699
Research Concepts (primary)1000
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
CanFollowWeakness BaseWeakness Base600Uncaught Exception in Servlet
Research Concepts1000
CanFollowWeakness ClassWeakness Class756Missing Custom Error Page
Research Concepts1000
CanAlsoBeWeakness VariantWeakness Variant81Improper Neutralization of Script in an Error Message Web Page
Research Concepts1000
CanAlsoBeWeakness VariantWeakness Variant201Information Exposure Through Sent Data
Research Concepts1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CLASPAccidental leaking of sensitive information through error messages
OWASP Top Ten 2007A6CWE More SpecificInformation Leakage and Improper Error Handling
OWASP Top Ten 2004A7CWE More SpecificImproper Error Handling
OWASP Top Ten 2004A10CWE More SpecificInsecure Configuration Management
CERT Java Secure CodingERR01-JDo not allow exceptions to expose sensitive information
CERT C++ Secure CodingERR12-CPPDo not allow exceptions to transmit sensitive information
Software Fault PatternsSFP23Exposed Data
+ References
Web Application Security Consortium. "Information Leakage". <>.
Brian Chess and Jacob West. "Secure Programming with Static Analysis". Section 9.2, page 326.. Addison-Wesley. 2007.
[REF-8] M. Howard and D. LeBlanc. "Writing Secure Code". Chapter 16, "General Good Practices." Page 415. 1st Edition. Microsoft. 2002.
[REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 11: Failure to Handle Errors Correctly." Page 183. McGraw-Hill. 2010.
[REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 12: Information Leakage." Page 191. McGraw-Hill. 2010.
Johannes Ullrich. "Top 25 Series - Rank 16 - Information Exposure Through an Error Message". SANS Software Security Institute. 2010-03-17. <>.
[REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 3, "Overly Verbose Error Messages", Page 75.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submission DateSubmitterOrganizationSource
CLASPExternally Mined
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITREInternal
updated Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings
2008-10-14CWE Content TeamMITREInternal
updated Relationships
2009-01-12CWE Content TeamMITREInternal
updated Demonstrative_Examples, Description, Name, Observed_Examples, Other_Notes, Potential_Mitigations, Relationships, Time_of_Introduction
2009-03-10CWE Content TeamMITREInternal
updated Demonstrative_Examples, Potential_Mitigations, Relationships
2009-12-28CWE Content TeamMITREInternal
updated Demonstrative_Examples, Name, Potential_Mitigations, References, Time_of_Introduction
2010-02-16CWE Content TeamMITREInternal
updated Detection_Factors, References, Relationships
2010-04-05CWE Content TeamMITREInternal
updated Related_Attack_Patterns
2010-06-21CWE Content TeamMITREInternal
updated Common_Consequences, Detection_Factors, Potential_Mitigations, References
Suggested OWASP Top Ten mapping
2010-09-27CWE Content TeamMITREInternal
updated Potential_Mitigations, Relationships
2011-03-29CWE Content TeamMITREInternal
updated Demonstrative_Examples, Observed_Examples, Relationships
2011-06-01CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2011-06-27CWE Content TeamMITREInternal
updated Relationships
2011-09-13CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated References, Related_Attack_Patterns, Relationships
2013-07-17CWE Content TeamMITREInternal
updated References
2014-06-23CWE Content TeamMITREInternal
updated Relationships
2014-07-30CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
Previous Entry Names
Change DatePrevious Entry Name
2009-01-12Error Message Information Leaks
2009-12-28Error Message Information Leak

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Page Last Updated: May 05, 2017