The Star Forge had a wide range of Defenses along with it's Defense Fleet; Thousands of Anti-Ship Heavy Turbolaser batteries, A million Point-defense Laser cannons and Ion Cannons; and so much more.
Within the Star Forge was enough space to house nearly two whole Fleets of Sith Warships; This technique was used in the battle over Sol, where it's escort fleet was replaced by a Stored Fleet inside. This, combined with the tenacity of the Sith and their advanced weapons and shielding, made it almost impossible to defeat them... the answer lied within the Star Forge itself.
Inside the Star Forge, a massive number of Sith Troopers and combat droids were used for inner defense; these were slowly cleared out by the UCR, UNSC, and Capitol Infiltration teams, whom were also aided by Rann Mano's party. Under the leadership of Marquis (Who gladly lead the UCR, but was reluctant in commanding the UNSC and Capitol), they managed to suffer less casualties to what was expected. However, almost everyone still was killed; they managed to push far enough to leave a somewhat easy path for Revan to get to the Bridge, while the infiltration team set out to destroy the Star Forge.However, this proved uneccessary, as upon Malak's defeat, he had manually set a Timed self destruct in an attempt to destroy not only the Fleets surrounding the Star Forge, but to also cause Sol to go Supernova with the massive surge of destruction right above it. This would have caused the entire System to be destroyed.
Fortunately, Revan, with the assistance of Rann's Party, managed to set it on a course that would lead far enough away from the Sun to keep the System from becoming extinct. Only with a Team of UNSC Marines, ODSTs, a handful of SPARTAN-III's and a few SPARTAN-IV's that stayed behind to direct the Superweapon away could victory and safety be assured; Revan took his personal Sith Starfighter and pursued a few Sith Warships that escaped into the far reaches of Space, while the Star Forge detonated with a massive explosion at a safe distance. Even though a mistake was made in how close the Star Forge was, the leftover mass of the destroyed Superweapon was pulled into the Sun via it's strong gravitational pull, restoring all the Mass that the Forge managed to take away.With this, the New Sith Wars had ended; the Galaxy was safe for now. The Star Forge was Destroyed. Sadly, there were no records left of the Sith upon their defeat.... all the pieces of the "Star Map" Required to find the Star Forge's destonation self-destructed in an EMP blast upon the Superweapon's demise, and all of the Sith Wreckages above Sol were burned up upon getting close enough due to Gravity.