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

Description

The product does not follow, or incorrectly follows, the chain of trust for a certificate back to a trusted root certificate.

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

Potential Impact

Non-Repudiation

Hide Activities

Integrity, Confidentiality, Availability, Access Control

Gain Privileges or Assume Identity, Execute Unauthorized Code or Commands

Demonstrative Examples

This code checks the certificate of a connected peer.

Bad

if ((cert = SSL_get_peer_certificate(ssl)) && host)foo=SSL_get_verify_result(ssl);
                     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 using an Adversary-in-the-Middle (AITM) attack to modify the traffic from server to client.

Mitigations & Prevention

Architecture and Design

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

Implementation

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

Implementation

If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the full chain of trust.

Detection Methods

Automated Static Analysis High — Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then sea

Real-World CVE Examples

CVE ID	Description
CVE-2016-2402	Server allows bypass of certificate pinning by sending a chain of trust that includes a trusted CA that is not pinned.
CVE-2008-4989	Verification function trusts certificate chains in which the last certificate is self-signed.
CVE-2012-5821	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).
CVE-2009-3046	Web browser does not check if any intermediate certificates are revoked.
CVE-2009-0265	chain: DNS server does not correctly check return value from the OpenSSL EVP_VerifyFinal function allows bypass of validation of the certificate chain.
CVE-2009-0124	chain: incorrect check of return value from the OpenSSL EVP_VerifyFinal function allows bypass of validation of the certificate chain.
CVE-2002-0970	File-transfer software does not validate Basic Constraints of an intermediate CA-signed certificate.
CVE-2002-0862	Cryptographic API, as used in web browsers, mail clients, and other software, does not properly validate Basic Constraints.

Taxonomy Mappings

CLASP: — Failure to follow chain of trust in certificate validation

Frequently Asked Questions

What is CWE-296?

CWE-296 (Improper Following of a Certificate's Chain of Trust) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. The product does not follow, or incorrectly follows, the chain of trust for a certificate back to a trusted root certificate.

How can CWE-296 be exploited?

Attackers can exploit CWE-296 (Improper Following of a Certificate's Chain of Trust) to hide activities. This weakness is typically introduced during the Implementation, Implementation phase of software development.

How do I prevent CWE-296?

Key mitigations include: Ensure that proper certificate checking is included in the system design.

What is the severity of CWE-296?

CWE-296 is classified as a Base-level weakness (Medium abstraction). It has been observed in 8 real-world CVEs.