CyberGhost VPN SHA-1 Signature Vulnerability and ASLR Bypass

A vulnerability exists in the CyberGhost VPN Windows installer, CyberGhostVPNSetup.exe, which is signed using the SHA-1 cryptographic hash algorithm. This signature method is susceptible to collision attacks, enabling a malicious actor to create a fake installer with a forged SHA-1 certificate that could be accepted by Windows signature verification, especially on systems with lenient SmartScreen or trust policy settings. Furthermore, the installer does not implement High Entropy Address Space Layout Randomization (ASLR), as verified by BinSkim and WinDbg. This absence of proper ASLR allows the binary to load into predictable memory addresses, which could be exploited to enhance the success of memory corruption attacks. Together, these flaws could facilitate supply-chain attacks or privilege escalation by tricking users into installing malicious software that appears legitimate.

Impact

Exploitation of these vulnerabilities could lead to a bypass of Windows' trust verification for signed applications, allowing the installation of malware disguised as a trusted program. The lack of High Entropy ASLR further increases the risk by making memory corruption exploits more reliable.

Reproduction

The vulnerability can be reproduced by creating a fake installer using a self-signed certificate with SHA-1 hashing. This can be done by generating a fake certificate with OpenSSL, signing a binary with that certificate using signtool.exe, and then observing that Windows accepts the signature as valid. The absence of High Entropy ASLR can be confirmed by using WinDbg to check the memory addresses where the CyberGhost VPN installer loads, which will show low, predictable addresses instead of the expected high, randomized ones.