CVE-2013-3900

Code Signing Myths: Why a Valid Digital Signature Does Not Equal File Safety

Digital signatures confirm only that a file was issued by a specific publisher at a given time and remained unchanged afterward. They do not verify current safety, the legitimacy of the current holder, or whether the private key was stolen months earlier. Attackers obtain legitimate certificates through build-system leaks, supply-chain compromises such as the 2019 ASUS ShadowHammer incident, or weak reseller validation. Expired certificates remain usable because verification can be performed at the timestamp recorded by an RFC 3161 TSA token rather than the current system clock. Signature hashes in Authenticode deliberately exclude the checksum field, certificate table, and attribute certificate table, allowing limited tampering that older WinVerifyTrust implementations did not fully block. Revocation checks are soft by default, and revocation dates can leave an exploitation window open. Organizations should enforce publisher thumbprint allow-lists in WDAC or AppLocker and store signing keys exclusively in HSMs.