There are various cases when during an IT/ security assurance projects there are specific requirements to rely on penetration testing projects/ reports completed by a third party.
However, not always, the IT security auditors have the necessary information to assess the quality of the penetration testing projects (focusing on planning, projects delivery and reporting).
And I address here the IT security assurance projects having in scope IT systems and finalizing with an Independent Auditor Report (IT Audit Opinion) and not audits focused on processes (like ISO audits) or on specific IT controls relevant for specific objectives (like ISAE 3402 IT/ Security assurance projects).
IT/ Security auditing standards
In order to have a consistent and objective assessment of third party reports, an IT security auditor must refer to the auditing standards he is using for performing his engagement.
And if we consider the IT audit standards available on the 
market, we must look at ISACA framework. There are also other standards applicable to various industries or specific objectives, focused on management systems, like ISO standards, but ISACA’s are the only ones of general nature which can be used cross-platforms, industries, etc. And as support for this, I performed some quick Internet searches and found mostly the same views.
For example, in one of its papers, NIST recognizes the entities enumerated below as addressing the IT auditing within their standards, further states that all of them taken essentially the same position concerning audits involving information systems and continues focusing on ISACA’s CobIT.
- The American Institute of Certified Public Accountants (AICPA) in several Statements on Auditing Standards (SASs);
- Institute of Internal Auditors Association (IIA) in its Standards for the Professional Practice of Internal Auditing;
- Information Systems Audit and Control Association (ISACA) in its “ITAF™: A Professional Practices Framework for IS Audit/Assurance”
- S. General Accounting Office (GAO) in its Government Auditing Standards and Title 2, Accounting.
