# NULL Pointer Dereference in setnmap() at cmds.c:2303 ## Description
A NULL Pointer Dereference was discovered in help() at inetutils/telnet/commands.c:3094. The vulnerability causes a segmentation fault and application crash. **version** ``` ./telnet --version telnet (GNU inetutils) 2.2.16-cf091 Copyright (C) 2021 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later < https://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Written by many authors. ``` **System information** Ubuntu 20.04 focal, AMD EPYC 7742 64-Core @ 16x 2.25GHz ## Proof of Concept **poc** ``` base64 poc ID8JCQn/CQn/CQj/////CQlkCQkJCQnwCQkJCQloCQkJCQn/////CQlkCQkJCQnwCQkJ7ekJCQkJ CQkJCeoICQkZCQkJKiwJCQkJCQkJCQkJCQk= ``` **command:** ``` ./ftp < ./poc ``` **Result** ``` ./telnet < poc telnet> ?Invalid help command � ?Invalid help command � ?Invalid help command���� display operating parameters ?Invalid help command � [3] 398703 segmentation fault ./telnet < poc ``` **gdb** ``` Breakpoint 2, 0x000055555555dbd3 in help (argc=8, argv=0x55555557c130 <margv+48>) at commands.c:3094 3094 printf ("%s\n", c->help); LEGEND: STACK | HEAP | CODE | DATA | RWX | RODATA ────────────────────────────────────────────[ REGISTERS ]───────────────────────────────────────────── *RAX 0x0 *RBX 0x55555557b480 (cmdtab2) —▸ 0x555555571232 ◂— 0x6f6400706c6568 /* 'help' */ RCX 0x0 *RDX 0xc6 *RDI 0x0 *RSI 0x5555555719cc ◂— 0x646f6d7263 /* 'crmod' */ R8 0x0 *R9 0x18 R10 0x555555572ee2 ◂— 0x2500454d4f48000a /* '\n' */ R11 0x246 *R12 0x55555557befd (line+29) ◂— 0xffff090909090068 /* 'h' */ R13 0x7fffffffe210 ◂— 0x1 R14 0x0 R15 0x0 RBP 0x7fffffffe060 —▸ 0x7fffffffe090 —▸ 0x7fffffffe120 ◂— 0x0 RSP 0x7fffffffe040 —▸ 0x55555557c130 (margv+48) —▸ 0x55555557befd (line+29) ◂— 0xffff090909090068 /* 'h' */ RIP 0x55555555dbd3 (help+212) ◂— call 0x555555559790 ──────────────────────────────────────────────[ DISASM ]────────────────────────────────────────────── 0x55555555dbcc <help+205> mov rax, qword ptr [rbx + 8] 0x55555555dbd0 <help+209> mov rdi, rax ► 0x55555555dbd3 <help+212> call puts@plt <puts@plt> s: 0x0 0x55555555dbd8 <help+217> sub dword ptr [rbp - 0x14], 1 0x55555555dbdc <help+221> cmp dword ptr [rbp - 0x14], 0 0x55555555dbe0 <help+225> jg help+116 <help+116> 0x55555555dbe2 <help+227> mov eax, 0 0x55555555dbe7 <help+232> add rsp, 0x10 0x55555555dbeb <help+236> pop rbx 0x55555555dbec <help+237> pop r12 0x55555555dbee <help+239> pop rbp ──────────────────────────────────────────[ SOURCE (CODE) ]─────────────────────────────────────────── In file: /root/disk2/fuzzing/inetutils/inetutils/telnet/commands.c 3089 if (Ambiguous (c)) 3090 printf ("?Ambiguous help command %s\n", arg); 3091 else if (c == (Command *) 0) 3092 printf ("?Invalid help command %s\n", arg); 3093 else ► 3094 printf ("%s\n", c->help); 3095 } 3096 return 0; 3097 } 3098 3099 static char *rcname = 0; ──────────────────────────────────────────────[ STACK ]─────────────────────────────────────────────── 00:0000│ rsp 0x7fffffffe040 —▸ 0x55555557c130 (margv+48) —▸ 0x55555557befd (line+29) ◂— 0xffff090909090068 /* 'h' */ 01:0008│ 0x7fffffffe048 ◂— 0x85557bee1 02:0010│ 0x7fffffffe050 —▸ 0x55555557b440 (cmdtab+480) —▸ 0x55555557121b ◂— 0x616c70736944003f /* '?' */ 03:0018│ 0x7fffffffe058 —▸ 0x555555559d20 (_start) ◂— endbr64 04:0020│ rbp 0x7fffffffe060 —▸ 0x7fffffffe090 —▸ 0x7fffffffe120 ◂— 0x0 05:0028│ 0x7fffffffe068 —▸ 0x55555555dab9 (command+550) ◂— test eax, eax 06:0030│ 0x7fffffffe070 ◂— 0x0 07:0038│ 0x7fffffffe078 ◂— 0x100000000 ────────────────────────────────────────────[ BACKTRACE ]───────────────────────────────────────────── ► f 0 0x55555555dbd3 help+212 f 1 0x55555555dab9 command+550 f 2 0x55555555e3c8 main+776 f 3 0x7ffff7db50b3 __libc_start_main+243 ────────────────────────────────────────────────────────────────────────────────────────────────────── pwndbg> bt #0 0x000055555555dbd3 in help (argc=8, argv=0x55555557c130 <margv+48>) at commands.c:3094 #1 0x000055555555dab9 in command (top=1, tbuf=0x0, cnt=0) at commands.c:3044 #2 0x000055555555e3c8 in main (argc=0, argv=0x7fffffffe220) at main.c:423 #3 0x00007ffff7db50b3 in __libc_start_main (main=0x55555555e0c0 <main>, argc=1, argv=0x7fffffffe218, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffffffe208) at ../csu/libc-start.c:308 #4 0x0000555555559d4e in _start () ``` crash ``` Program received signal SIGSEGV, Segmentation fault. __strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:65 65 ../sysdeps/x86_64/multiarch/strlen-avx2.S: No such file or directory. LEGEND: STACK | HEAP | CODE | DATA | RWX | RODATA ────────────────────────────────────────────[ REGISTERS ]───────────────────────────────────────────── RAX 0x0 RBX 0x55555557b480 (cmdtab2) —▸ 0x555555571232 ◂— 0x6f6400706c6568 /* 'help' */ RCX 0x0 *RDX 0x0 RDI 0x0 RSI 0x5555555719cc ◂— 0x646f6d7263 /* 'crmod' */ R8 0x0 R9 0x18 R10 0x555555572ee2 ◂— 0x2500454d4f48000a /* '\n' */ R11 0x246 *R12 0x0 R13 0x7fffffffe210 ◂— 0x1 R14 0x0 R15 0x0 RBP 0x7fffffffe060 —▸ 0x7fffffffe090 —▸ 0x7fffffffe120 ◂— 0x0 *RSP 0x7fffffffe008 —▸ 0x7ffff7e155b4 (puts+20) ◂— mov r13, qword ptr [rip + 0x16398d] *RIP 0x7ffff7f19675 (__strlen_avx2+21) ◂— vpcmpeqb ymm1, ymm0, ymmword ptr [rdi] ──────────────────────────────────────────────[ DISASM ]────────────────────────────────────────────── ► 0x7ffff7f19675 <__strlen_avx2+21> vpcmpeqb ymm1, ymm0, ymmword ptr [rdi] 0x7ffff7f19679 <__strlen_avx2+25> vpmovmskb eax, ymm1 0x7ffff7f1967d <__strlen_avx2+29> test eax, eax 0x7ffff7f1967f <__strlen_avx2+31> jne __strlen_avx2+272 <__strlen_avx2+272> ↓ 0x7ffff7f19770 <__strlen_avx2+272> tzcnt eax, eax 0x7ffff7f19774 <__strlen_avx2+276> add rax, rdi 0x7ffff7f19777 <__strlen_avx2+279> sub rax, rdx 0x7ffff7f1977a <__strlen_avx2+282> vzeroupper 0x7ffff7f1977d <__strlen_avx2+285> ret 0x7ffff7f1977e <__strlen_avx2+286> nop 0x7ffff7f19780 <__strlen_avx2+288> tzcnt eax, eax ──────────────────────────────────────────────[ STACK ]─────────────────────────────────────────────── 00:0000│ rsp 0x7fffffffe008 —▸ 0x7ffff7e155b4 (puts+20) ◂— mov r13, qword ptr [rip + 0x16398d] 01:0008│ 0x7fffffffe010 —▸ 0x55555557b480 (cmdtab2) —▸ 0x555555571232 ◂— 0x6f6400706c6568 /* 'help' */ 02:0010│ 0x7fffffffe018 —▸ 0x7fffffffe060 —▸ 0x7fffffffe090 —▸ 0x7fffffffe120 ◂— 0x0 03:0018│ 0x7fffffffe020 —▸ 0x55555557befd (line+29) ◂— 0xffff090909090068 /* 'h' */ 04:0020│ 0x7fffffffe028 —▸ 0x7fffffffe210 ◂— 0x1 05:0028│ 0x7fffffffe030 ◂— 0x0 06:0030│ 0x7fffffffe038 —▸ 0x55555555dbd8 (help+217) ◂— sub dword ptr [rbp - 0x14], 1 07:0038│ 0x7fffffffe040 —▸ 0x55555557c130 (margv+48) —▸ 0x55555557befd (line+29) ◂— 0xffff090909090068 /* 'h' */ ────────────────────────────────────────────[ BACKTRACE ]───────────────────────────────────────────── ► f 0 0x7ffff7f19675 __strlen_avx2+21 f 1 0x7ffff7e155b4 puts+20 f 2 0x55555555dbd8 help+217 f 3 0x55555555dab9 command+550 f 4 0x55555555e3c8 main+776 f 5 0x7ffff7db50b3 __libc_start_main+243 ```