I am not a C developer so I have to guess here.

For me it looks like the static address of buff is returned by ip_addr2a.

char *ip_addr2a(struct ip_addr *ip)
{
	static char buff[IP_ADDR_MAX_STR_SIZE];
        // ...
	return buff;
}

-- https://github.com/kamailio/kamailio/blob/1535031a6c992c23270050793b23d290a631b684/src/core/ip_addr.c#L267C1-L276C2

If that's the case, I think every user of that function should copy the value from that address instead of remembering the address. Otherwise it is always the same address for every call of ip_addr2a and subsequent calls overwrite the value of the previous call.

Unfortunately, the sipcapture module uses the returned value directly:

si->address_str.s = ip_addr2a(&si->address);

-- https://github.com/kamailio/kamailio/blob/1535031a6c992c23270050793b23d290a631b684/src/modules/sipcapture/hep.c#L487C2-L487C46

I tested with the following code and I think it confirms my theory because foo changes to "bar".

#include <stdio.h>
#include <string.h>

char *a(char* in);

int main() {
  char *foo = a("foo");
  printf("foo %08x -> %08x = %s\n", &foo, foo, foo);

  char *bar = a("bar");
  printf("foo %08x -> %08x = %s\n", &foo, foo, foo);
  printf("bar %08x -> %08x = %s\n", &bar, bar, bar);
}

char *a(char* in) {
  static char out[10];
  strcpy(out, in);
  return out;
}

Output:

foo 0c3399d8 -> b37ba018 = foo
foo 0c3399d8 -> b37ba018 = bar
bar 0c3399e0 -> b37ba018 = bar

However, I can't explain why this should be any different in previous kamailio versions.

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