Add RUSTSEC advisory for rkyv issue #644

Author: shinmao

crates/rkyv/RUSTSEC-0000-0000.md

@@ -0,0 +1,20 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "rkyv"
+date = "2026-01-05"
+url = "https://github.com/rkyv/rkyv/issues/644"
+categories = ["memory-corruption"]
+keywords = ["oom", "undefined-behavior"]
+
+[versions]
+patched = [">= 0.8.13"]
+```
+
+# Potential Undefined Behaviors in `Arc<T>`/`Rc<T>` impls of `from_value` on OOM
+
+The `SharedPointer::alloc` implementation for `sync::Arc<T>` and `rc::Rc<T>` in `rkyv/src/impls/alloc/rc/atomic.rs` (and `rc.rs`) does not check if the allocator returns a null pointer on OOM (Out of Memory).
+
+This null pointer can flow through to `SharedPointer::from_value`, which calls `Box::from_raw(ptr)` with the null pointer. This triggers undefined behavior when utilizing safe deserialization APIs (such as `rkyv::from_bytes` or `rkyv::deserialize_using`) if an OOM condition occurs during the allocation of the shared pointer.
+
+The issue is reachable through safe code and violates Rust's safety guarantees.