A Use After Free vulnerability in command processing of Juniper Networks Junos OS on MX Series allows a local, authenticated attacker to cause the broadband edge service manager daemon (bbe-smgd) to crash upon execution of specific CLI commands, creating a Denial of Service (DoS) condition. The process crashes and restarts automatically.
When specific CLI commands are executed, the bbe-smgd daemon attempts to write into an area of memory (mgd socket) that was already closed, causing the process to crash. This process manages and controls the configuration of broadband subscriber sessions and services. While the process is unavailable, additional subscribers will not be able to connect to the device, causing a temporary Denial of Service condition.
This issue only occurs if Graceful Routing Engine Switchover (GRES) and Subscriber Management are enabled. This issue affects Junos OS:
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.