SimulationCraft: Heap-Based Buffer Overflow / Out-of-Bounds Write in SimulationCraft's gem_id Array

Summary

SimulationCraft is a tool to explore combat mechanics in World of Warcraft. In builds after release-820-01 and before the identified May 7, 2026 nightly, the `bcp_api.cpp` loop over the JSON `sockets` array uses `slot_data["sockets"].Size()` without bounding `gem_idx` by `MAX_GEM_SLOTS`, which is four in `engine/sc_enums.hpp`. The destination `gem_id` and `gem_bonus_id` arrays in `engine/item/item.hpp` have only four elements. More than four socket entries therefore write beyond `gem_id` into the adjacent `gem_bonus_id` vector storage; `bonus_list` entries can also access `gem_bonus_id` out of bounds. Corrupting a vector's `_M_start` pointer causes the `item_t` destructor to free an attacker-influenced pointer during normal cleanup. The advisory reports crashes and code execution demonstrated in a testing environment. Attack inputs can arrive through a malicious `.simc` profile with a `[[equipment]]` section, a compromised addon export, or `Battle.net API` responses modified by an attacker with a privileged network position. The fix is contained in the nightly build identified as simc-1205-01-516b5d7; no containing release tag is available.