anti
9777aa7677
Plugs the cred-coverage gap for MongoDB. The template previously
parsed only the wire opcode + length and discarded the BSON body
entirely, so SCRAM-SHA-{1,256} client-proofs flowed straight through
without ever landing in the Credential table.
Adds an inline minimal BSON walker (~100 LoC) covering the 7 type
codes auth commands actually use: string, doc, array, binary, bool,
int32, int64. Hand-rolled rather than pulling pymongo as a runtime
dep — the parser is bounds-checked for untrusted-input safety
(won't loop on malformed length fields).
Wire flow MongoDB clients use for auth:
- OP_MSG body section (kind=0) → BSON doc with `saslStart` field
carrying mechanism + payload (SCRAM client-first-message:
"n,,n=<user>,r=<nonce>"). Username extracted, pinned to the
per-connection _sasl_username + _sasl_mechanism state.
- Subsequent OP_MSG with `saslContinue` → SCRAM client-final-message
("c=biws,r=<combined>,p=<base64 client-proof>"). The `p=` value is
the credential — emitted as secret_kind=scram_sha256 (or _sha1 /
_unknown depending on the prior saslStart's mechanism), principal
= the pinned username, secret_b64 = base64 of the decoded proof.
Reuse semantics: same client-proof across two auth attempts only
matches when both server salt and password were identical (proofs
include the salt). So cross-session reuse correlates only on
credential reuse against the same MongoDB account on the same decky
— honest, non-misleading signal.
680 tests pass across services, service_testing, db, web/ingester,
and core/fingerprinting (the broader scope my recent commits
touched). Phases 4, 5, 7 still pending (RDP basic-auth, SMB
NTLMSSP, RDP NLA).
353 lines
12 KiB
Python
353 lines
12 KiB
Python
#!/usr/bin/env python3
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"""
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MongoDBserver.
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Implements the MongoDB wire protocol OP_MSG/OP_QUERY handshake. Responds
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to isMaster/hello, listDatabases, and authenticate commands. Logs all
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received messages as JSON.
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"""
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import asyncio
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import base64
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import os
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import struct
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import instance_seed as _seed
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from syslog_bridge import syslog_line, write_syslog_file, forward_syslog
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# ─── Minimal BSON walker ──────────────────────────────────────────────────────
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# Just enough to extract `saslStart` / `saslContinue` command auth fields.
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# Pulls a few BSON type codes; ignores everything else (subdocs returned
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# as raw bytes the caller can re-parse if needed). Hand-rolled rather
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# than pulling pymongo as a runtime dep — we only need 8 type codes and
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# the parser is ~40 LoC.
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_BSON_DOUBLE = 0x01
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_BSON_STRING = 0x02
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_BSON_DOC = 0x03
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_BSON_ARRAY = 0x04
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_BSON_BINARY = 0x05
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_BSON_BOOL = 0x08
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_BSON_INT32 = 0x10
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_BSON_INT64 = 0x12
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def _bson_read(buf: bytes, off: int = 0) -> dict:
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"""Read a single BSON document at ``buf[off]``. Returns a dict of
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``{key: value}``. Lossy on unsupported types (silently skipped).
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Untrusted-input safe: bounds-checked, won't infinite-loop on
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malformed length fields."""
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out: dict = {}
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if off + 4 > len(buf):
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return out
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doc_len = struct.unpack_from("<i", buf, off)[0]
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end = off + doc_len
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if end > len(buf) or doc_len < 5:
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return out
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p = off + 4
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while p < end - 1: # last byte is the trailing 0x00
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t = buf[p]
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p += 1
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if t == 0:
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break
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# Read NUL-terminated cstring key.
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nul = buf.find(b"\x00", p, end)
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if nul < 0:
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break
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key = buf[p:nul].decode("utf-8", errors="replace")
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p = nul + 1
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if t == _BSON_STRING:
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if p + 4 > end:
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break
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slen = struct.unpack_from("<i", buf, p)[0]
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p += 4
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if p + slen > end or slen < 1:
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break
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out[key] = buf[p:p + slen - 1].decode("utf-8", errors="replace")
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p += slen
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elif t == _BSON_BINARY:
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if p + 5 > end:
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break
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blen = struct.unpack_from("<i", buf, p)[0]
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p += 4
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_subtype = buf[p]
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p += 1
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if p + blen > end or blen < 0:
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break
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out[key] = buf[p:p + blen] # raw bytes
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p += blen
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elif t == _BSON_INT32:
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if p + 4 > end:
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break
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out[key] = struct.unpack_from("<i", buf, p)[0]
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p += 4
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elif t == _BSON_INT64:
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if p + 8 > end:
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break
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out[key] = struct.unpack_from("<q", buf, p)[0]
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p += 8
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elif t == _BSON_BOOL:
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if p + 1 > end:
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break
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out[key] = buf[p] != 0
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p += 1
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elif t == _BSON_DOUBLE:
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p += 8
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elif t in (_BSON_DOC, _BSON_ARRAY):
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if p + 4 > end:
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break
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sub_len = struct.unpack_from("<i", buf, p)[0]
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if p + sub_len > end:
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break
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p += sub_len
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else:
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# Unsupported type — abort cleanly so we don't misalign.
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break
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return out
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def _scram_kv(payload: bytes) -> dict:
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"""Parse a SCRAM message into key=value pairs. SCRAM separates by
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commas and uses `name=value` pairs. We strip a leading `n,,` (GS2
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header) when present so the `n=username` shows up directly."""
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s = payload.decode("utf-8", errors="replace")
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if s.startswith("n,,"):
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s = s[3:]
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elif s.startswith("y,,"):
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s = s[3:]
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out: dict = {}
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for part in s.split(","):
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if "=" in part:
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k, _, v = part.partition("=")
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out[k.strip()] = v
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return out
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NODE_NAME = os.environ.get("NODE_NAME", "mongodb")
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SERVICE_NAME = "mongodb"
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LOG_TARGET = os.environ.get("LOG_TARGET", "")
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PORT = int(os.environ.get("PORT", "27017"))
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# Per-instance (version, maxWireVersion) — paired per real MongoDB release.
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# Wire version is locked to major/minor per upstream release notes.
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_MONGO_RELEASES = [
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("4.4.22", 9),
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("5.0.25", 13),
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("6.0.5", 17),
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("6.0.14", 17),
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("7.0.5", 21),
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("7.0.8", 21),
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("7.0.11", 21),
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]
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_MONGO_VERSION, _MONGO_WIRE = _seed.pick(_MONGO_RELEASES)
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_MONGO_SET_NAME = os.environ.get("MONGO_REPL_SET", "") # empty = standalone
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def _new_objectid() -> bytes:
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"""12-byte BSON ObjectId — fresh per call."""
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return _seed.fresh_bytes(12)
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# Minimal BSON helpers
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def _bson_str(key: str, val: str) -> bytes:
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k = key.encode() + b"\x00"
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v = val.encode() + b"\x00"
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return b"\x02" + k + struct.pack("<I", len(v)) + v
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def _bson_int32(key: str, val: int) -> bytes:
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return b"\x10" + key.encode() + b"\x00" + struct.pack("<i", val)
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def _bson_bool(key: str, val: bool) -> bytes:
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return b"\x08" + key.encode() + b"\x00" + (b"\x01" if val else b"\x00")
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def _bson_doc(*fields: bytes) -> bytes:
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body = b"".join(fields) + b"\x00"
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return struct.pack("<I", len(body) + 4) + body
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def _op_reply(request_id: int, doc: bytes) -> bytes:
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# OP_REPLY header: total_len(4), req_id(4), response_to(4), opcode(4)=1,
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# flags(4), cursor_id(8), starting_from(4), number_returned(4), docs
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header = struct.pack(
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"<iiiiiqii",
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16 + 20 + len(doc), # total length
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0, # request id
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request_id, # response to
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1, # OP_REPLY
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0, # flags
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0, # cursor id (int64)
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0, # starting from
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1, # number returned
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)
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return header + doc
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def _op_msg(request_id: int, doc: bytes) -> bytes:
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payload = b"\x00" + doc
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flag_bits = struct.pack("<I", 0)
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msg_body = flag_bits + payload
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header = struct.pack("<iiii",
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16 + len(msg_body),
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1,
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request_id,
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2013,
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)
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return header + msg_body
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def _log(event_type: str, severity: int = 6, **kwargs) -> None:
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line = syslog_line(SERVICE_NAME, NODE_NAME, event_type, severity, **kwargs)
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write_syslog_file(line)
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forward_syslog(line, LOG_TARGET)
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class MongoDBProtocol(asyncio.Protocol):
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def __init__(self):
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self._transport = None
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self._peer = None
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self._buf = b""
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# Per-connection SCRAM state: pinned at saslStart so the
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# subsequent saslContinue's client-proof can carry the username
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# in the emitted credential row.
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self._sasl_username: str | None = None
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self._sasl_mechanism: str | None = None
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def connection_made(self, transport):
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self._transport = transport
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self._peer = transport.get_extra_info("peername", ("?", 0))
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_log("connect", src=self._peer[0], src_port=self._peer[1])
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def data_received(self, data):
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self._buf += data
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while len(self._buf) >= 16:
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msg_len = struct.unpack("<I", self._buf[:4])[0]
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if msg_len < 16 or msg_len > 48 * 1024 * 1024:
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self._transport.close()
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self._buf = b""
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return
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if len(self._buf) < msg_len:
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break
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msg = self._buf[:msg_len]
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self._buf = self._buf[msg_len:]
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self._handle_message(msg)
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def _handle_message(self, msg: bytes):
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if len(msg) < 16:
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return
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request_id = struct.unpack("<I", msg[4:8])[0]
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opcode = struct.unpack("<I", msg[12:16])[0]
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_log("message", src=self._peer[0], opcode=opcode, length=len(msg))
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# SCRAM cred capture: parse the OP_MSG body BSON looking for
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# saslStart / saslContinue. Each fires its own log event:
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# saslStart pins the username + mechanism; saslContinue emits
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# the credential row with the client-proof as secret_b64.
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if opcode == 2013 and len(msg) >= 21:
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# OP_MSG body: 4 bytes flagBits, then sections. We only
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# parse kind=0 (Body) sections — kind=1 (DocSeq) is for
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# bulk ops that don't carry SCRAM auth.
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p = 20 # 16 hdr + 4 flagBits
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while p < len(msg):
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kind = msg[p]
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p += 1
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if kind == 0: # Body section
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if p + 4 > len(msg):
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break
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doc_len = struct.unpack_from("<i", msg, p)[0]
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if p + doc_len > len(msg):
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break
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cmd = _bson_read(msg, p)
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self._handle_command(cmd)
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p += doc_len
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elif kind == 1: # DocSeq — skip
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if p + 4 > len(msg):
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break
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seq_len = struct.unpack_from("<i", msg, p)[0]
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p += seq_len
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else:
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break
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# Build a generic isMaster-style OK response with this instance's
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# version pair. Fresh topologyVersion on every reply (matches real
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# mongod behavior — clients use this to detect failover).
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fields = [
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_bson_bool("ismaster", True),
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_bson_bool("helloOk", True),
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_bson_int32("maxBsonObjectSize", 16777216),
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_bson_int32("maxMessageSizeBytes", 48000000),
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_bson_int32("maxWriteBatchSize", 100000),
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_bson_int32("maxWireVersion", _MONGO_WIRE),
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_bson_int32("minWireVersion", 0),
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_bson_str("version", _MONGO_VERSION),
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_bson_int32("ok", 1),
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]
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if _MONGO_SET_NAME:
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fields.insert(1, _bson_str("setName", _MONGO_SET_NAME))
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reply_doc = _bson_doc(*fields)
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if opcode == 2013: # OP_MSG
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self._transport.write(_op_msg(request_id, reply_doc))
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else:
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self._transport.write(_op_reply(request_id, reply_doc))
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def _handle_command(self, cmd: dict) -> None:
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"""Parse a single MongoDB command document for SCRAM auth.
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saslStart — client-first-message in payload. Extract
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`n=<username>` so the next saslContinue inherits it.
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saslContinue — client-final-message in payload. Extract
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`p=<base64 client-proof>` and emit a cred row.
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"""
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# mongo's command dispatch keys off the FIRST field of the BSON
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# document. We just check key presence since dict ordering in
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# CPython 3.7+ matches insertion order.
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if "saslStart" in cmd:
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mechanism = cmd.get("mechanism")
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payload = cmd.get("payload") or b""
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if isinstance(mechanism, str):
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self._sasl_mechanism = mechanism
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if isinstance(payload, (bytes, bytearray)):
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kv = _scram_kv(bytes(payload))
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self._sasl_username = kv.get("n")
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_log("auth_start", src=self._peer[0],
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mechanism=mechanism or "?",
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username=self._sasl_username or "")
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return
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if "saslContinue" in cmd:
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payload = cmd.get("payload") or b""
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if not isinstance(payload, (bytes, bytearray)):
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return
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kv = _scram_kv(bytes(payload))
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proof_b64 = kv.get("p")
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if not proof_b64:
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return
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try:
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proof_raw = base64.b64decode(proof_b64, validate=True)
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except (ValueError, base64.binascii.Error):
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return
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mech = (self._sasl_mechanism or "").upper()
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if "SHA-256" in mech or "SHA256" in mech:
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kind = "scram_sha256"
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elif "SHA-1" in mech or "SHA1" in mech:
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kind = "scram_sha1"
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else:
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kind = "scram_unknown"
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_log("auth", src=self._peer[0],
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username=self._sasl_username or "",
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principal=self._sasl_username,
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mechanism=self._sasl_mechanism or "",
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secret_kind=kind,
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secret_printable=proof_b64,
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secret_b64=base64.b64encode(proof_raw).decode("ascii"))
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return
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def connection_lost(self, exc):
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_log("disconnect", src=self._peer[0] if self._peer else "?")
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async def main():
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_log("startup", msg=f"MongoDB server starting as {NODE_NAME}")
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loop = asyncio.get_running_loop()
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server = await loop.create_server(MongoDBProtocol, "0.0.0.0", PORT) # nosec B104
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async with server:
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await server.serve_forever()
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if __name__ == "__main__":
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asyncio.run(main())
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