If the effect is consistent with this lens and your other lenses are fine, the problem is most likely inside the lens rather than the camera body. A common cause on the EF 28-70mm f/2.8L is internal element haze from deteriorated cement in a lens group, which can create blooming/glow around bright highlights even when the outer glass looks clean. It’s generally not the same as visible dust, and one community reply specifically noted it is not fungus.

First, rule out temporary condensation if the lens was moved between very different temperatures or humidity levels. If the haze is repeatable, the lens likely needs service.

Because this appears to be an internal optical issue, cleaning the front or rear element will not fix it. Repair may require replacing the affected optical group, often using parts from another lens. If Canon no longer supports this model, an independent repair shop experienced with older Canon L lenses may be the best option.