Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
Home > CWE List > CWE- Individual Dictionary Definition (2.11)  

CWE-296: Improper Following of a Certificate's Chain of Trust

Weakness ID: 296
Abstraction: Base
Status: Draft
Presentation Filter:
+ Description

Description Summary

The software does not follow, or incorrectly follows, the chain of trust for a certificate back to a trusted root certificate, resulting in incorrect trust of any resource that is associated with that certificate.

Extended Description

If a system does not follow the chain of trust of a certificate to a root server, the certificate loses all usefulness as a metric of trust. Essentially, the trust gained from a certificate is derived from a chain of trust -- with a reputable trusted entity at the end of that list. The end user must trust that reputable source, and this reputable source must vouch for the resource in question through the medium of the certificate.

In some cases, this trust traverses several entities who vouch for one another. The entity trusted by the end user is at one end of this trust chain, while the certificate-wielding resource is at the other end of the chain. If the user receives a certificate at the end of one of these trust chains and then proceeds to check only that the first link in the chain, no real trust has been derived, since the entire chain must be traversed back to a trusted source to verify the certificate.

There are several ways in which the chain of trust might be broken, including but not limited to:

  • Any certificate in the chain is self-signed, unless it the root.

  • Not every intermediate certificate is checked, starting from the original certificate all the way up to the root certificate.

  • An intermediate, CA-signed certificate does not have the expected Basic Constraints or other important extensions.

  • The root certificate has been compromised or authorized to the wrong party.

+ Time of Introduction
  • Architecture and Design
+ Applicable Platforms



+ Common Consequences

Technical Impact: Hide activities

Exploitation of this flaw can lead to the trust of data that may have originated with a spoofed source.

Access Control

Technical Impact: Gain privileges / assume identity; Execute unauthorized code or commands

Data, requests, or actions taken by the attacking entity can be carried out as a spoofed benign entity.

+ Likelihood of Exploit


+ Demonstrative Examples

Example 1

This code checks the certificate of a connected peer.

(Bad Code)
Example Languages: C and C++ 
if ((cert = SSL_get_peer_certificate(ssl)) && host)
if ((X509_V_OK==foo) || X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN==foo))
// certificate looks good, host can be trusted

In this case, because the certificate is self-signed, there was no external authority that could prove the identity of the host. The program could be communicating with a different system that is spoofing the host, e.g. by poisoning the DNS cache or conducting a man-in-the-middle attack.

+ Observed Examples
Verification function trusts certificate chains in which the last certificate is self-signed.
Chain: Web browser uses a TLS-related function incorrectly, preventing it from verifying that a server's certificate is signed by a trusted certification authority (CA).
Web browser does not check if any intermediate certificates are revoked.
chain: DNS server does not correctly check return value from the OpenSSL EVP_VerifyFinal function allows bypass of validation of the certificate chain.
chain: incorrect check of return value from the OpenSSL EVP_VerifyFinal function allows bypass of validation of the certificate chain.
File-transfer software does not validate Basic Constraints of an intermediate CA-signed certificate.
Cryptographic API, as used in web browsers, mail clients, and other software, does not properly validate Basic Constraints.
+ Potential Mitigations

Phase: Architecture and Design

Ensure that proper certificate checking is included in the system design.

Phase: Implementation

Understand, and properly implement all checks necessary to ensure the integrity of certificate trust integrity.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness BaseWeakness Base295Improper Certificate Validation
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfWeakness ClassWeakness Class573Improper Following of Specification by Caller
Research Concepts1000
ChildOfCategoryCategory724OWASP Top Ten 2004 Category A3 - Broken Authentication and Session Management
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory948SFP Secondary Cluster: Digital Certificate
Software Fault Pattern (SFP) Clusters (primary)888
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
PeerOfWeakness BaseWeakness Base370Missing Check for Certificate Revocation after Initial Check
Research Concepts1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CLASPFailure to follow chain of trust in certificate validation
+ 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. <>.
[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
2010-12-13CWE Content TeamMITREInternal
updated 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, Other_Notes, References, Relationships
2013-07-17CWE Content TeamMITREInternal
updated Relationships
2014-07-30CWE Content TeamMITREInternal
updated Demonstrative_Examples, Relationships
Previous Entry Names
Change DatePrevious Entry Name
2009-03-10Failure to Follow Chain of Trust in Certificate Validation
2013-02-21Improper Following of Chain of Trust for Certificate Validation

More information is available — Please select a different filter.
Page Last Updated: May 05, 2017