It looks like lens flare. It is an internal reflection inside the lens. It is caused by off axis light allowed to fall on the front surface if the lens from outside the field of view.

For an example of such flare when the exposure is brightened please see: Can you photograph the milky way with a full moon out?

It might also be sunlight reflecting off dust that has been kicked up by the astronaut. In the moon's gravity field that is only 1/6 as strong as that of the Earth's the same amount of force would cause the dust to go 6x higher before falling back to the surface and it would also take 6x as long for such dust to settle as it would in a vacuum under Earth's gravity. There is also no atmosphere and thus no wind to disperse the dust.

It might be possible that dust could be electrostatically stuck to the front of the lens in some of the photos taken on the surface of the moon. In the case of the Apollo 11 photo of Buzz Aldrin descending the ladder of the LEM the absence of such a smudge in photos taken subsequently argues strongly against that theory. The Apollo 11 mission only included a single EVA, so all photos of Aldrin on the Moon's surface were necessarily taken after the photo of him coming down the ladder of the LEM.

This image was 34 frames later from the same film magazine on the same camera as the shot of Buzz descending the ladder:

Notice that there is no evidence of dust on the lens. If one examines all of the images from that magazine it quickly becomes apparent that the angle of the sun to the camera and whether the camera is in the shade of the LEM or not are the most determining factors regarding which images demonstrate the effect and which ones don't.

Likewise, if one examines all of the images in sequence from film magazine LL on the Apollo 14 mission it becomes abundantly clear that lens flare is the main culprit.