Two Russian servicemen were indeed killed in a mortar/rocket attack on Russia's airbase in Latakia but the rest of the story seems to be baloney.

Rumors are starting to flow about an alleged attack on the Russian Aerospace Forces airbase in Khmeimin, Syria. I have been parsing the Russian news sources and here is what I can say so far:

an attack did indeed take place it was a combined multiple rocket launcher and mortar attack the rockets were all intercepted and destroyed the mortars did land and inflict damage the original report was based on one single Russian “diplomatic source” the original claim was four Su-24 bombers, two Su-35S fighters and an An-72 transport plane, as well as an ammunition depot the original claim also said that 10 Russians personnel were wounded

It appears that the reality is much less dramatic: mortars did land on the periphery of the base. However 2 soldiers were killed and 7 wounded. At this point in time, it does not appear that any aircraft were hit. Apparently the photos of damaged aircraft posted in the Russian social media have been taken elsewhere. The Russian MoD as specifically denied the veracity of this rumor and called it a ‘fake’.

As a rule, I would never say never.

However, I note that so far:

nobody has shown any footage, not even from cellphones, of the attack nobody has shown any footage of the aftermath neither the USA nor even the Takfiris (Daesh/ISIS/IS/al-Qaeda/New Syrian Army/etc.) claims that attack in the past, the Russians always reported their failures (SU-24, shot down helo, etc.) normally when attacked, the Russians admit it and make promises of merciless retaliation

It is, however, true that the Russian aircraft at Khmeimim are not under shelter and that is not a good thing.

Conclusion: at this point in time (0105UTC) I am calling this either a fake or a big exaggeration.