Adds advisory for unsoundness in fragile

crates/fragile/RUSTSEC-0000-0000.md

@@ -0,0 +1,42 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "fragile"
+date = "2025-03-23"
+url = "https://github.com/mitsuhiko/fragile/issues/34"
+informational = "unsound"
+categories = ["memory-corruption"]
+keywords = ["fragile", "sticky"]
+
+[versions]
+patched = []
+unaffected = []
+
+[affected]
+```
+
+# Possible use after free when using `slab` feature of `fragile`.
+
+When the `slab` feature of `fragile` is enable it allows for dropping values still referenced.
+The following example is taken from https://github.com/mitsuhiko/fragile/issues/34 . 
+
+```rust
+fn main() {
+    let dummy_sticky = thread::spawn(|| Sticky::new(())).join().unwrap();
+
+    let sticky_string = ManuallyDrop::new(Sticky::new(String::from("Hello World")));
+    stack_token!(t);
+
+    let hello: &str = sticky_string.get(t);
+
+    println!("now it exists: {hello}");
+    drop(dummy_sticky);
+    println!("now it's gone: {hello}");
+}
+```
+```
+now it exists: Hello World
+now it's gone: -[L\�Jx
+```
+
+Recommended fix is to disable the `slab` feature or switch to another crate like [`send_wrapper`](https://crates.io/crates/send_wrapper).