Presented at
DEF CON 31 (2023),
Aug. 12, 2023, 2 p.m.
(45 minutes)
Digital signatures are fundamental for verifying the authenticity and integrity of untrusted data in the digital world. They ensure that software, firmware, and other digital content are not tampered with during transmission or at rest. Code signing certificates are significantly more challenging to obtain when compared to alternatives like SSL or S/MIME certificates. The latter only has a single criterion- proof of control over a domain, while the former requires significant validation of the publisher itself.
This project uncovered a systemic vulnerability present in numerous signature validation implementations, enabling attackers to exploit valid certificates in an unintended manner. Vulnerable implementations mistakenly perceive files signed with incompatible certificates as legitimate, violating their respective specifications and allowing threat actors to sign untrusted code at little to no cost. In this talk, we will explore the problem at all levels, ranging from the fundamental theory to its application across multiple formats and real-world situations.
REFERENCES:
- Boeyen, Sharon, et al. “Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile.” IETF, 1 May 2008, datatracker.ietf.org/doc/html/rfc5280.
- Housley, Russ. “Cryptographic Message Syntax (CMS).” IETF, 5 Sept. 2002, datatracker.ietf.org/doc/html/rfc3369.
- “Windows Authenticode Portable Executable Signature Format.” Microsoft.com, Microsoft, 21 Mar. 2008, download.microsoft.com/download/9/c/5/9c5b2167-8017-4bae-9fde-d599bac8184a/authenticode_pe.docx.
- “PE Format - Win32 Apps.” Learn.microsoft.com, Microsoft, 31 Mar. 2021, learn.microsoft.com/en-us/windows/win32/debug/pe-format.
- “Trusted Root Certification Authorities Certificate Store.” Learn.microsoft.com, Microsoft, 14 Dec. 2021, learn.microsoft.com/en-us/windows-hardware/drivers/install/trusted-root-certification-authorities-certificate-store.
- “What’s the Difference between DV, OV & EV SSL Certificates?” Www.digicert.com, DigiCert, 23 Aug. 2022, www.digicert.com/difference-between-dv-ov-and-ev-ssl-certificates.
- The OpenSSL Project. OpenSSL: The Open Source Toolkit for SSL/TLS. Apr. 2003.
- Brubaker, Chad, et al. “Using Frankencerts for Automated Adversarial Testing of Certificate Validation in SSL/TLS Implementations.” 2014 IEEE Symposium on Security and Privacy, 18 May 2014, www.cs.cornell.edu/~shmat/shmat_oak14.pdf, https://doi.org/10.1109/sp.2014.15.
Presenters:
-
Bill Demirkapi
- Microsoft Security Response Center
Bill is an undergraduate student and a security researcher for the Microsoft Security Response Center with an intense passion for Windows Internals. His interests include reverse engineering and vulnerability research, ranging from low-level memory corruption to systemic flaws with catastrophic consequences. He started his journey in high school and has since published his work at internationally-recognized conferences like DEF CON and Black Hat USA. In his pursuit to make the world a better place, Bill constantly looks for the next significant vulnerability, following the motto "break anything and everything".
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