CVE-2021-44647: 
Memcached vulnerability analysis and mitigation

Lua v5.4.3 and above are affected by a SEGV (Segmentation Fault) vulnerability caused by type confusion in the funcnamefromcode function within ldebug.c, which can result in a local denial of service (CVE Details, Debian Tracker).

The vulnerability occurs during error handling in the close metamethod of to-be-closed variables after calling os.exit. The main cause is that L->ci->previous->func value is located above L->top in the luaD_seterrorobj function. When os.exit function calls the close metamethod of tbc (to-be-closed), the upper callinfo frame calls the lower callinfo frame. The crash occurs when retrieving the name of the function that called the function in which the error occurred during the error handling process (Lua Users).

The vulnerability can cause a local denial of service through a segmentation fault in the Lua interpreter (CVE Details).

The issue was fixed in Lua 5.4.4 by modifying the state closing process. The fix involves unwinding the CallInfo list before closing protected calls by adding 'L->ci = &L->baseci' in the closestate function (Lua Users).