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CWE-297: Improper Validation of Certificate with Host Mismatch

Weakness ID: 297
Abstraction: Variant
Status: Incomplete
Presentation Filter:
+ Description

Description Summary

The software communicates with a host that provides a certificate, but the software does not properly ensure that the certificate is actually associated with that host.

Extended Description

Even if a certificate is well-formed, signed, and follows the chain of trust, it may simply be a valid certificate for a different site than the site that the software is interacting with. If the certificate's host-specific data is not properly checked - such as the Common Name (CN) in the Subject or the Subject Alternative Name (SAN) extension of an X.509 certificate - it may be possible for a redirection or spoofing attack to allow a malicious host with a valid certificate to provide data, impersonating a trusted host. In order to ensure data integrity, the certificate must be valid and it must pertain to the site that is being accessed.

Even if the software attempts to check the hostname, it is still possible to incorrectly check the hostname. For example, attackers could create a certificate with a name that begins with a trusted name followed by a NUL byte, which could cause some string-based comparisons to only examine the portion that contains the trusted name.

+ Time of Introduction
  • Architecture and Design
+ Applicable Platforms



Architectural Paradigms

Mobile Application

+ Common Consequences
Access Control

Technical Impact: Gain privileges / assume identity

The data read from the system vouched for by the certificate may not be from the expected system.


Technical Impact: Other

Trust afforded to the system in question -- based on the expired certificate -- may allow for spoofing or redirection attacks.

+ Likelihood of Exploit


+ Demonstrative Examples

Example 1

The following OpenSSL code obtains a certificate and verifies it.

(Bad Code)
Example Languages: C and C++ 
cert = SSL_get_peer_certificate(ssl);
if (cert && (SSL_get_verify_result(ssl)==X509_V_OK)) {
// do secret things

Even though the "verify" step returns X509_V_OK, this step does not include checking the Common Name against the name of the host. That is, there is no guarantee that the certificate is for the desired host. The SSL connection could have been established with a malicious host that provided a valid certificate.

+ Observed Examples
Mobile banking application does not verify hostname, leading to financial loss.
Mobile application for printing documents does not verify hostname, allowing attackers to read sensitive documents.
Software for electronic checking does not verify hostname, leading to financial loss.
Cloud-support library written in Python uses incorrect regular expression when matching hostname.
Web browser does not correctly handle '\0' character (NUL) in Common Name, allowing spoofing of https sites.
Database program truncates the Common Name during hostname verification, allowing spoofing.
Incorrect handling of '\0' character (NUL) in hostname verification allows spoofing.
Mail server's incorrect handling of '\0' character (NUL) in hostname verification allows spoofing.
LDAP server's incorrect handling of '\0' character (NUL) in hostname verification allows spoofing.
Payment processing module does not verify hostname when connecting to PayPal using PHP fsockopen function.
Smartphone device does not verify hostname, allowing spoofing of mail services.
E-commerce module does not verify hostname when connecting to payment site.
Chat application does not validate hostname, leading to loss of privacy.
Application uses third-party library that does not validate hostname.
Cloud storage management application does not validate hostname.
Java library uses JSSE SSLSocket and SSLEngine classes, which do not verify the hostname.
SOAP platform does not verify the hostname.
PHP library for payments does not verify the hostname.
Merchant SDK for payments does not verify the hostname.
Web browser does not validate Common Name, allowing spoofing of https sites.
+ Potential Mitigations

Phase: Architecture and Design

Check for expired certificates and provide the user with adequate information about the nature of the problem and how to proceed.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness BaseWeakness Base295Improper Certificate Validation
Development Concepts (primary)699
Research Concepts1000
Weaknesses for Simplified Mapping of Published Vulnerabilities (primary)1003
ChildOfWeakness ClassWeakness Class923Improper Restriction of Communication Channel to Intended Endpoints
Research Concepts (primary)1000
ChildOfCategoryCategory948SFP Secondary Cluster: Digital Certificate
Software Fault Pattern (SFP) Clusters (primary)888
PeerOfWeakness BaseWeakness Base370Missing Check for Certificate Revocation after Initial Check
Research Concepts1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CLASPFailure to validate host-specific certificate data
+ References
Martin Georgiev, Subodh Iyengar, Suman Jana, Rishita Anubhai, Dan Boneh and Vitaly Shmatikov. "The Most Dangerous Code in the World: Validating SSL Certificates in Non-Browser Software". 2012-10-25. <>.
Sascha Fahl, Marian Harbach, Thomas Muders, Matthew Smith and Lars Baumgärtner, Bernd Freisleben. "Why Eve and Mallory Love Android: An Analysis of Android SSL (In)Security". 2012-10-16. <>.
Kenneth Ballard. "Secure programming with the OpenSSL API, Part 2: Secure handshake". 2005-05-03. <>.
Eric Rescorla. "An Introduction to OpenSSL Programming (Part I)". 2001-10-05. <>.
[REF-17] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 23: Improper Use of PKI, Especially SSL." Page 347. McGraw-Hill. 2010.
+ Content History
Submission DateSubmitterOrganizationSource
CLASPExternally Mined
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings
2009-03-10CWE Content TeamMITREInternal
updated Description, Name, Relationships
2009-05-27CWE Content TeamMITREInternal
updated Demonstrative_Examples
2009-07-27CWE Content TeamMITREInternal
updated Demonstrative_Examples, Relationships
2010-12-13CWE Content TeamMITREInternal
updated Description, Other_Notes
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2012-05-11CWE Content TeamMITREInternal
updated References, Relationships
2013-02-21CWE Content TeamMITREInternal
updated Applicable_Platforms, Demonstrative_Examples, Description, Name, Observed_Examples, References, Relationships, Type
2013-07-17CWE Content TeamMITREInternal
updated Relationships
2014-07-30CWE Content TeamMITREInternal
updated Relationships
2015-12-07CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2009-03-10Failure to Validate Host-specific Certificate Data
2013-02-21Improper Validation of Host-specific Certificate Data

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Page Last Updated: May 05, 2017