I made my VM think it has a CPU fan

Original Article ↗ Hacker News Discussion ↗

Malware, AV, and VM Detection Tricks

  • Calling obscure system APIs (e.g., WMI fan queries) is seen as a “cute” but often counterproductive malware evasion trick: easy to spot statically and mark as suspicious, especially when used by small binaries.
  • Static regex-style pattern matching against such APIs was reported as surprisingly effective for catching mass-distributed malware.
  • Others point out malware is frequently signed nowadays, often with stolen certs or via vulnerable signed drivers, so “signed == trusted” is unreliable.
  • Goal of environment checks is often to avoid detonating a second-stage payload on an analyst VM, not to avoid AV detection entirely.

Should Everything Run in a VM?

  • Some argue we should run all untrusted software in VMs (Qubes-style, or even serverless like AWS Lambda).
  • Objections: hardware acceleration, I/O, and anti-cheat/DRM use-cases push toward more direct hardware access; malware already checks for VM artifacts and may self-delete when detected.
  • Others note that GPU and PCIe virtualization (SR-IOV, S-IOV) and Windows sandboxing are making “VM by default” more practical, even for consumers.

Hardware Virtualization and SR-IOV Debate

  • Long subthread debates whether SR-IOV/S-IOV meaningfully preserves isolation or just expands attack surface by giving guests “direct” hardware access.
  • One side stresses:
    • You’re now relying on complex, often closed firmware in NICs/GPUs/etc. to enforce partitioning correctly.
    • Compared to traditional software-only device emulation, this enlarges the security boundary.
  • The other side argues:
    • This is still virtualization with access control enforced in hardware (like VT-x/VT-d); you already depend on CPU/chipset microcode the same way.
    • The specs are explicitly about isolating functions, even if the implementation quality varies.
  • Consensus in the thread is unresolved; the disagreement is about degree of risk, not basic mechanics.

SMBIOS, Firmware, and Detection Reliability

  • Multiple reports of consumer boards with garbage or default SMBIOS fields (“to be filled by OEM”), reused UUIDs, and inconsistent cooling-device entries.
  • This suggests SMBIOS-based VM detection may misclassify a significant number of real machines, though malware can tolerate some failure if it always evades sandboxes.
  • Linux fan/temperature handling is described as a combination of ACPI plus many board-specific hwmon drivers.

Sandboxing / OS and App Permissions Ideas

  • Proposed: make real OSes look like VMs, and gate any “bare-metal” capabilities behind permissions that can return fake/random data.
  • That would force malware to either treat hosts like analysis VMs (reducing impact) or limit itself to a smaller target set.
  • Counterpoints:
    • Implementing this comprehensively is an enormous engineering task with hardware support implications.
    • Existing permission systems (Android, mobile, Flatpak, macOS sandbox) show users quickly habituate to granting access, and dev ecosystems are optimized for “it just works,” not least privilege.
    • Capability-based OSes like Genode/SculptOS already explore this paradigm; interesting but niche.

Honeypots and High-Fidelity Emulation

  • Practitioners emphasize how much work goes into making malware honeypots indistinguishable from real systems: old Windows versions, PLCs, thermostats, banker desktops, etc.
  • Suggestions include simulating realistic sensor behavior (temperature tracking CPU load, noisy GPS/IMU/barometer) to fool more sophisticated checks.

AV Heuristics and Trust Models

  • Some criticize AV products for heuristic/statistical guessing that causes false positives, arguing it’s not far from an implicit allowlist of big vendors.
  • Others note that in practice, much of the ecosystem already operates as “assume safe until shown otherwise,” often sending binaries to large vendors for cloud analysis.

Language and Tone of the Article

  • A substantial subthread reacts to the “smol pp way of thinking” joke.
  • Some readers found it funny and appropriate for a personal blog; others found it body-shaming, male-targeted, and a reminder the author assumes a male audience.
  • There’s a meta-debate about:
    • Whether calling this out improves inclusivity and mental health (e.g., around body insecurity).
    • Whether personal blogs should be “policed” for tone vs. being last bastions of informal/free expression.
    • HN guidelines cautioning against focusing discussion on provocative side remarks instead of technical content.

Other Notes

  • Several comments praise the technical depth and creativity of the writeup; some readers say it reminds them how large the “ocean” of expertise is.
  • People note parallels to Hackintosh SMBIOS spoofing and suggest tools that broadly emulate hardware/CPUID to defeat VM checks.
  • There are tangents about passive cooling builds, Streacom fanless cases, industrial vs. consumer PCs, and the general messiness of PC firmware.