CWE-296: Improper Following of a Certificate's Chain of Trust
Weakness ID: 296
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.
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
Technical Impact: Hide activities
Exploitation of this flaw can lead to the trust of data that may have
originated with a spoofed source.
Technical Impact: Gain privileges / assume
identity; Execute unauthorized code or
Data, requests, or actions taken by the attacking entity can be
carried out as a spoofed benign entity.
Likelihood of Exploit
This code checks the certificate of a connected peer.
Example Languages: C and C++
if ((cert = SSL_get_peer_certificate(ssl)) &&
if ((X509_V_OK==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
Failure to follow chain of trust in certificate
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. <http://www.cs.utexas.edu/~shmat/shmat_ccs12.pdf>.
[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.