Weaknesses. Like most other Symbiotes, it is vulnerable to sound and fire. However Carnage doesn't mind heat as long as it's the one making it.
More recently, Carnage gained additional power through the Darkhold, an ancient book of black magic written by the elder god Chthon. After that, the traditional weaknesses of a symbiote, including sonics and fire, didn't affect Carnage.
Weakness. Extreme Heat: Carnage's symbiote, like Venom's, was weak against extreme heat, but not as much as the latter: When Spider-Man electrocuted him on the electrified trail, Carnage was briefly weakened by the burns, but it's also angered him as he retaliates by slamming them against the wall.
Kasady is also immune to the effects of all Earthly diseases and infections as long as he remains bonded with the symbiote. Like Venom, Carnage is vulnerable to sound (to a much smaller degree than Venom) and heat (to a much larger degree than Venom), and is undetectable to Spider-Man's spider-sense.
Symbiotes like Venom are immensely powerful, possessed of great strength and endurance, but they also have two extremely common weaknesses: fire and sound. Numerous foes have used these to best Venom and other symbiotes, and Peter Parker even originally repelled the symbiote suit by exposing it to a tolling bell.
Like most other Symbiotes, it is vulnerable to sound and fire.
The other Celestials then banished Knull, along with the severed Celestial head, deeper into space. After that, he started using the head's cosmic energies as a forge for the symbiotes, which is how they developed the weaknesses to sound and fire.
In addition, Venom has come out on top as the victor in many battles with Symbiotes like Carnage, Hybrid, and Scream (all of which are arguably more powerful than he is).
The best chances are iron man, Thor, Scarlett witch, and black venom. Carnage has bitten through adamantium but not vibranium so enough kinetic blasts might work. Scarlett witch can just wipe him from existence. Thor has resisted symbiote a before and carnage has never been shown handling anything like his god blast.
The main reason was because the Carnage symbiote was not a perfect match with Cletus like Venom was with Eddie. In the middle of the climactic battle, we see Carnage and Cletus arguing with each other over Cletus' one true love Shriek, who Carnage hates because of her symbiote-killing sonic scream.
Who would win in a fight between carnage and riot? Carnage does have more abilities, but was like a rampaging kid and Venom ate it to kill it. Riot was cunning, and was even able to rip Venom from Brock and would have eaten him if Brock didn't rebond with it.
Carnage's foremost enemies include Eddie Brock, host to Carnage's parent symbiote Venom, and Spider-Man, who sometimes team up in an uneasy alliance to go up against the psychopathic Super Villain.
Venom Eats Carnage - Fight Scene - Venom 2: Let There Be Carnage (2021) - YouTube.
Venom's Weaknesses
The Venom symbiote has two major weaknesses - sound and fire. Loud noises cause the symbiote to writhe in pain.
Both Venom and Carnage feared the potential power of Toxin, establishing him as a force to be reckoned with. The character was created by writer Peter Milligan and artist Clayton Crain.
The fires of the forge and the sound of Knull's celestial hammer instilled a terror deep within the symbiote, and that fear turned into weakness that stayed with the entire Klyntar race eons after it was introduced.
Minimum Carnage
This Venom and Carnage battle took them to the Microverse, where Carnage had taken control. The only way Venom can beat him is if he stops fighting with Scarlet Spider and they work together to overcome the murderous villain.
Why does Venom hate Carnage? Carnage is a psychopath. Venom also, at times, does not want the symbiote to spread, and has actively hunted down other symbiotes. And to build on what you are saying, Venom also feels responsible for Carnage.
The original Carnage symbiote was the first offspring of the Venom symbiote, spawned when it broke Eddie Brock out of prison. The newborn symbiote bonded to serial killer Cletus Kasady, merging with his blood to become nigh-inseparable from him, and Carnage was born.
Carnage. Perhaps the Marvel Universe's deadliest symbiote, Carnage debuted in AMAZING SPIDER-MAN (1963) #345. Shortly after spawning from Venom, the Carnage symbiote bonded to a serial killer named Cletus Kasady.
Blue Symbiote (2) (Agony): In the comics Agony was one of the symbiotes forcibly spawned from Venom alongside several others by the Life Foundation.
Lasher is a largely green and light aqua symbiote.
The Anti-Venom Symbiote (of Earth-616) is a white version of the symbiote that was attached to Eddie Brock as a result of a regular symbiote merging with his white blood cells.