QIF-T0086

Ambient light sensor side-channel exfiltration (screen content inference via reflected light)

Ambient light sensors (ALS) in smartphones and tablets are low-resolution photometers (typically 16-bit, 10-100 Hz) that measure environmental illumination for auto-brightness. Since the ALS is near the display, it also captures light reflected back from the display itself and from nearby surfaces illuminated by the display. This creates a side channel: the ALS output correlates with screen content. While the ALS cannot reconstruct a full image, it can distinguish between dark and light screens, detect page scrolling patterns, identify video content by temporal light signatures, and in some cases infer text content via character-level luminance patterns. Crucially, ALS access requires no permission on most mobile platforms — it's treated as a low-risk environmental sensor. This makes it an unrestricted exfiltration channel for screen activity patterns.