CVE-2025-32381: xgrammar Vulnerable to Denial of Service (DoS) by abusing unbounded cache in memory

The vulnerability is an unbounded cache in xgrammar. The provided patch information from commit ef8d18d653366ea7eff736ac38918af32acf4728 (part of PR #243 which fixes the issue) modifies cpp/support/thread_safe_cache.h. Specifically, it shows changes to the ThreadSafeCacheSized2::GetFuture method. This method is responsible for fetching items from the cache or, if not present, computing them and adding them to the cache. The core of the vulnerability lies in the step where new items are added to the cache's underlying storage (an std::unordered_map) without checking if the cache has exceeded a size limit. The line auto [it, success] = map.try_emplace(key); within GetFuture (or its equivalent in the vulnerable code) is where this insertion happens. The class ThreadSafeCacheSized2 and the commit message suggest this is the fixed, size-aware version. Therefore, the vulnerable function is the logical predecessor or the unfixed version of this GetFuture method, which performed the cache insertion without bounds checking, leading to the DoS.