Deno is a JavaScript, TypeScript, and WebAssembly runtime. Starting in version 1.36.2 and prior to version 1.40.3, use of inherently unsafe *const c_void and ExternalPointer leads to use-after-free access of the underlying structure, resulting in arbitrary code execution. Use of inherently unsafe *const c_void and ExternalPointer leads to use-after-free access of the underlying structure, which is exploitable by an attacker controlling the code executed inside a Deno runtime to obtain arbitrary code execution on the host machine regardless of permissions. This bug is known to be exploitable for both *const c_void and ExternalPointer implementations. Version 1.40.3 fixes this issue.
Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.
The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:
In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.