In this lesson,
we're going to explore Certificate Transparency or CT log
and their role in enhancing digital certificate security.
We'll discuss how these logs help prevent malicious
or mistakenly issued certificates
from compromising network communications
and why they are important
in maintaining a secure web environment.
Certificate Transparency is an open framework
developed by Google
that provides a publicly auditable record
issued digital certificate.
The primary goal is to prevent malicious
or mistakenly issued certificates from going unnoticed,
which could otherwise be exploited by attackers
to perform On-path or Man-in-the-Middle attacks.
Next, we'll discuss how Certificate Transparency logs
work in practice.
All publicly trusted Certificate Authorities or CAs
are required to submit newly issued SSL/TLS certificates
to publicly accessible CT logs.
Each certificate entry contains a timestamp
and a cryptographic signature,
ensuring its authenticity and integrity.
Monitors constantly scan the CT logs
for any suspicious certificates
that could indicate a malicious or mistaken issuance.
Organizations can run their own monitors
to detect certificates
that have been issued for their domains
without their authorization.
Auditors verify that logs are operating correctly
by checking the consistency and validity of log entries.
They ensure that logs are tamper-resistant
and that no certificate entries are removed or altered.
Certificate Transparency sits within the broader ecosystem
of the Web Public Key Infrastructure,
which includes everything required
to issue and verify certificates used for TLS on the web.
Web PKI certificates bind a public cryptographic key
to a domain name,
similar to how a passport links a person's photo and name.
CAs issue these certificates,
making them a key part in Web PKI.
However, the system requires domain owners
and user agents (typically web browsers)
to trust that CAs are correctly associating certificates
with the proper domain owners.
A hacked or negligent CA
can issue certificates for any website,
creating a potential risk of a Man-in-the-Middle (MitM)
also known as an On-path attack,
even though the communication remains technically encrypted.
Rogue certificates are certificates that are issued
without the domain owner's authorizations.
By monitoring CT logs,
organizations can detect rouge certificates
and take immediate action to revoke them.
For example, in 2015,
Google's monitoring of CT logs
led to discovery of unauthorized certificates
issued by CNNIC,
or China Internet Network Information Center.
These certificates were quickly revoked,
preventing potential on-path attacks.
Certificate misissuance occurs
when a CA mistakenly issues a certificate
for a domain without proper validation.
CT logs provide transparency and accountability,
allowing domain owners to monitor certificate issuance
and report misissued certificates.
A misissuance incident occurred in 2017
when it was discovered that Symantec
had misissued over 30,000 certificates.
Google's CT logs played a key role
in uncovering these violations,
leading to the deprecation of Symantec's root certificates
and popular web browsers.
When it comes to pentesting,
Certificate Transparency logs are useful
during the reconnaissance phase,
providing testers with a lot of actionable intelligence.
Penetration testers can utilize CT logs
to uncover unknown subdomains
and hidden services within a company's digital landscape,
often revealing poorly secured or outdated subdomains
that could serve as potential entry points for attackers.
For example, a pentester might use CT logs
to discover that a subdomain like dev.diontraining.com
has not been documented.
A subsequent scan could reveal a vulnerable web application
running on default credentials,
presenting a significant security risk.
Pen testers also use CT logs
to understand the client certificate landscape better.
This involves identifying certificates
that are expired or soon to expire,
which might suggest lapses
in the client certificate management practices.
Additionally, testers look for certificate
that uses weak encryption algorithms
or that are misconfigured,
such as those employing deprecated SHA-1 encryption.
This analysis helps highlight security weaknesses
that need to be addressed.
Pentesters also map out a client's external infrastructure
through detailed examination of the CT logs.
This includes identifying the range
of certificate authorities the client uses,
and spotting dependencies
between services based on certificate issuance patterns.
Mappings like this can reveal things
about the organizational structure
and indicate which subdomains
and services are prioritized.
CT logs also help in identifying domains
that are susceptible to phishing
and could be targeted for social engineering attacks.
So remember, Certificate Transparency logs
are not just for passive observation;
they are a potent tool in the hands of a skilled pentester.
By integrating CT log analysis into their methodologies,
testers can offer comprehensive assessments
that help clients fortify their defenses
against sophisticated cyber threats.