halcy0nic/cve-2022-44318Prova di concetto per CVE-2022-44318
È stato scoperto che PicoC versione 3.2.2 contiene un heap buffer overflow nella funzione StringStrcat in cstdlib/string.c quando viene chiamata da ExpressionParseFunctionCall. Qualsiasi progetto o libreria che utilizza Picoc è affetto da questo problema. Un esempio è picoc-js.
Per replicare la vulnerabilità di heap overflow in PicoC, dobbiamo prima scaricare e compilare una versione vulnerabile (v3.2.2) della libreria e dell'interprete PicoC:
git clone https://github.com/jpoirier/picoc.git
cd picoc
git checkout a97d94fa3d4d35c6b78b7de69faac7643e34de22
make
Eseguire l'interprete in modalità script sul file StringStrcat_heap_overflow.c incluso in questo repository:
$ ./picoc -s StringStrcat_heap_overflow.c
Otterrai un segfault e il programma andrà in crash. Questo è il risultato di un heap overflow che non viene intercettato o gestito dalla libreria o dall'interprete. Possiamo ricompilare il progetto con l'address sanitizer (ASAN) per avere un'idea migliore di dove avviene il problema. Aggiungiamo -fsanitize=address alla variabile CFLAGS nel Makefile e ricompiliamo la libreria:
CFLAGS=-Wall -g -std=gnu11 -pedantic -DUNIX_HOST -DVER=\"`git show-ref --abbrev=8 --head --hash head`\" -DTAG=\"`git describe --abbrev=0 --tags`\" -fsanitize=address
Ricompilare la libreria e l'interprete (dalla directory principale picoc):
make clean
make
Quando eseguiamo il nostro programma, otteniamo il seguente output da ASAN che ci mostra che l'heap buffer overflow avviene in StringStrcat cstdlib/string.c, riga 40:
==308939==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x606000000892 at pc 0x7f489c03a590 bp 0x7ffc052778f0 sp 0x7ffc052770a0
WRITE of size 26 at 0x606000000892 thread T0
#0 0x7f489c03a58f in __interceptor_strcat ../../../../src/libsanitizer/asan/asan_interceptors.cpp:392
#1 0x55facf0eb418 in StringStrcat cstdlib/string.c:40
#2 0x55facf0d4edd in ExpressionParseFunctionCall /dev/shm/picoc/expression.c:1909
#3 0x55facf0d237c in ExpressionParse /dev/shm/picoc/expression.c:1607
#4 0x55facf0c66a0 in ParseStatement /dev/shm/picoc/parse.c:646
#5 0x55facf0c8380 in PicocParse /dev/shm/picoc/parse.c:897
#6 0x55facf0e0d0e in PicocPlatformScanFile platform/platform_unix.c:129
#7 0x55facf0b7213 in main /dev/shm/picoc/picoc.c:62
#8 0x7f489be46189 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
#9 0x7f489be46244 in __libc_start_main_impl ../csu/libc-start.c:381
#10 0x55facf0b6d40 in _start (/dev/shm/picoc/picoc+0x16d40)
0x606000000892 is located 0 bytes to the right of 50-byte region [0x606000000860,0x606000000892)
allocated by thread T0 here:
#0 0x7f489c0ae987 in __interceptor_calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:154
#1 0x55facf0d5b80 in HeapAllocMem /dev/shm/picoc/heap.c:127
#2 0x55facf0da3a9 in VariableAlloc /dev/shm/picoc/variable.c:77
#3 0x55facf0da429 in VariableAllocValueAndData /dev/shm/picoc/variable.c:97
#4 0x55facf0da701 in VariableAllocValueFromType /dev/shm/picoc/variable.c:119
#5 0x55facf0dbaa7 in VariableDefine /dev/shm/picoc/variable.c:303
#6 0x55facf0dc6aa in VariableDefineButIgnoreIdentical /dev/shm/picoc/variable.c:383
#7 0x55facf0c4540 in ParseDeclaration /dev/shm/picoc/parse.c:366
#8 0x55facf0c6f6e in ParseStatement /dev/shm/picoc/parse.c:738
#9 0x55facf0c8380 in PicocParse /dev/shm/picoc/parse.c:897
#10 0x55facf0e0d0e in PicocPlatformScanFile platform/platform_unix.c:129
#11 0x55facf0b7213 in main /dev/shm/picoc/picoc.c:62
#12 0x7f489be46189 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
SUMMARY: AddressSanitizer: heap-buffer-overflow ../../../../src/libsanitizer/asan/asan_interceptors.cpp:392 in __interceptor_strcat
Shadow bytes around the buggy address:
0x0c0c7fff80c0: fa fa fa fa fd fd fd fd fd fd fd fa fa fa fa fa
0x0c0c7fff80d0: 00 00 00 00 00 00 06 fa fa fa fa fa 00 00 00 00
0x0c0c7fff80e0: 00 00 00 00 fa fa fa fa 00 00 00 00 00 00 05 fa
0x0c0c7fff80f0: fa fa fa fa 00 00 00 00 00 00 02 fa fa fa fa fa
0x0c0c7fff8100: 00 00 00 00 00 00 00 00 fa fa fa fa 00 00 00 00
=>0x0c0c7fff8110: 00 00[02]fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c0c7fff8120: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c0c7fff8130: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c0c7fff8140: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c0c7fff8150: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c0c7fff8160: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
Addressable: 00
Partially addressable: 01 02 03 04 05 06 07
Heap left redzone: fa
Freed heap region: fd
Stack left redzone: f1
Stack mid redzone: f2
Stack right redzone: f3
Stack after return: f5
Stack use after scope: f8
Global redzone: f9
Global init order: f6
Poisoned by user: f7
Container overflow: fc
Array cookie: ac
Intra object redzone: bb
ASan internal: fe
Left alloca redzone: ca
Right alloca redzone: cb
Shadow gap: cc
==308939==ABORTING
void StringStrcat(struct ParseState *Parser, struct Value *ReturnValue,
struct Value **Param, int NumArgs)
{
ReturnValue->Val->Pointer = strcat(Param[0]->Val->Pointer,
Param[1]->Val->Pointer);
}