rust-openssl is a set of OpenSSL bindings for the Rust programming language. In affected versions ssl::select_next_proto can return a slice pointing into the server arguments buffer but with a lifetime bound to the client argument. In situations where the sever buffers lifetime is shorter than the client buffers, this can cause a use after free. This could cause the server to crash or to return arbitrary memory contents to the client. The crateopenssl version 0.10.70 fixes the signature of ssl::select_next_proto to properly constrain the output buffers lifetime to that of both input buffers. Users are advised to upgrade. In standard usage of ssl::select_next_proto in the callback passed to SslContextBuilder::set_alpn_select_callback, code is only affected if the server buffer is constructed within the callback.
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.