ISC2 Certified Secure Software Lifecycle Professional (CSSLP) Practice Question
During threat modeling for a cloud document-sharing service, you identify a misuse case: an attacker uploads malware disguised as "report.pdf.exe" to bypass extension filtering. Which security requirement most effectively mitigates this threat before the file is stored?
The platform must enforce TLS 1.2 or higher for all client connections.
The application must inspect the file header (magic number) to confirm it matches the declared MIME type before accepting the upload.
All uploaded files must be encrypted at rest using AES-256 within one hour of storage.
The system must limit each upload to a maximum of 25 MB to conserve storage resources.
Relying on the client-supplied extension alone is insufficient, because an attacker can append a benign extension to a malicious executable (double-extension attack). The most effective countermeasure is server-side validation that inspects the binary signature or magic number and ensures it matches the claimed MIME type. If the header does not correspond to an allowed format, the upload is rejected, neutralizing the exploit path. Transport encryption, encryption at rest, or file-size limits provide confidentiality or resource controls but do not stop malicious content from entering the system. Logging improves detection after the fact but does not prevent the initial compromise.
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ISC2 Certified Secure Software Lifecycle Professional (CSSLP)
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