RUSTSEC-2026-0253: Potential use-after-free due to lack of panic safety in LruCache::pop() #105

Potential use-after-free due to lack of panic safety in LruCache::pop()

LruCache::pop() in lru was not panic-safe. If the Drop implementation of a stored key panics during pop(), self.detach() is never called, leaving dangling pointers in the internal doubly-linked list.

A subsequent cache operation that triggers eviction can then dereference these dangling pointers:

• The node is freed from the map, but remains linked in the LRU list due to the skipped detach() call
• When a new insertion causes eviction, the LRU traversal encounters the dangling pointer
• This results in a write to already-freed memory during the eviction process

Impact

• CWE-416 (Use-After-Free): memory corruption when subsequent cache operations access freed node pointers in the linked list
• CWE-415 (Double Free): potential heap corruption when the same memory is freed multiple times

Both types of undefined behavior can be invoked in safe Rust, but only if unwinding panics are enabled and std::panic::catch_unwind is used with key types that have potentially-panicking Drop implementations.

Fix

Fixed in lru 0.18.2 by detaching the node from the linked list before freeing it and dropping the key (lru-rs#238).

See advisory page for additional details.