GHSA-98qm-wvgf-w4cf — MongoDB Python Driver: Out-of-bounds read in BSON decoding via a malformed Regex element

MongoDB Python Driver: Out-of-bounds read in BSON decoding via a malformed Regex element

The advisory, in context

Impact

The C extension's BSON decoder scans a Regex element's pattern and flags strings with strlen before checking the document's remaining length, so a crafted truncated Regex element can read past the end of the caller's buffer. bson.decode and bson.decode_all accept mmap and array buffers, which carry no NUL sentinel; the read can cross into unmapped memory and kill the process with an uncatchable SIGSEGV. Any application decoding untrusted BSON from such buffers is affected — impact is availability only, since the out-of-bounds bytes are never returned as content. NUL-terminated buffers (bytes, bytearray) raise InvalidBSON at worst; the driver's own transport and pure-Python installs are not affected. All releases through 4.18.2 are affected when the C extension is loaded.

Patches

Fixed in PyMongo 4.18.3. Malformed Regex elements now raise InvalidBSON on every accepted buffer type; valid documents decode unchanged.

Workarounds

Decode untrusted BSON only from NUL-terminated buffers — bytes or bytearray — and copy mmap input first, e.g. bytes(mm[:size]).

Affected packages

Start with the recorded fix for your release branch. Check your installed version and test compatibility before upgrading. Fixing this advisory does not rule out other vulnerabilities in the release.

pymongo PyPI

Ecosystem versions

From 3.9.0 before 4.18.3

Fixed in 4.18.3

64 explicitly affected versions

3.10.0, 3.10.1, 3.11.0, 3.11.1, 3.11.2, 3.11.3, 3.11.4, 3.12.0, 3.12.1, 3.12.2, 3.12.3, 3.13.0, 3.9.0, 4.0, 4.0.1, 4.0.2, 4.1.0, 4.1.1, 4.10.0, 4.10.1, 4.11, 4.11.1, 4.11.2, 4.11.3, 4.12.0, 4.12.1, 4.13.0, 4.13.0.dev0, 4.13.1, 4.13.2, 4.14.0, 4.14.1, 4.15.0, 4.15.1, 4.15.2, 4.15.3, 4.15.4, 4.15.5, 4.16.0, 4.16.0.dev0, 4.17.0, 4.18.0, 4.18.1, 4.18.2, 4.2.0, 4.3.2, 4.3.3, 4.4.0, 4.4.0b0, 4.4.1, 4.5.0, 4.6.0, 4.6.1, 4.6.2, 4.6.3, 4.7.0, 4.7.1, 4.7.2, 4.7.3, 4.8.0, 4.8.0b0, 4.9, 4.9.1, 4.9.2

View affected-version evidence

{
  "ranges": [
    {
      "events": [
        {
          "introduced": "3.9.0"
        },
        {
          "fixed": "4.18.3"
        }
      ],
      "type": "ECOSYSTEM"
    }
  ],
  "versions": [
    "3.10.0",
    "3.10.1",
    "3.11.0",
    "3.11.1",
    "3.11.2",
    "3.11.3",
    "3.11.4",
    "3.12.0",
    "3.12.1",
    "3.12.2",
    "3.12.3",
    "3.13.0",
    "3.9.0",
    "4.0",
    "4.0.1",
    "4.0.2",
    "4.1.0",
    "4.1.1",
    "4.10.0",
    "4.10.1",
    "4.11",
    "4.11.1",
    "4.11.2",
    "4.11.3",
    "4.12.0",
    "4.12.1",
    "4.13.0",
    "4.13.0.dev0",
    "4.13.1",
    "4.13.2",
    "4.14.0",
    "4.14.1",
    "4.15.0",
    "4.15.1",
    "4.15.2",
    "4.15.3",
    "4.15.4",
    "4.15.5",
    "4.16.0",
    "4.16.0.dev0",
    "4.17.0",
    "4.18.0",
    "4.18.1",
    "4.18.2",
    "4.2.0",
    "4.3.2",
    "4.3.3",
    "4.4.0",
    "4.4.0b0",
    "4.4.1",
    "4.5.0",
    "4.6.0",
    "4.6.1",
    "4.6.2",
    "4.6.3",
    "4.7.0",
    "4.7.1",
    "4.7.2",
    "4.7.3",
    "4.8.0",
    "4.8.0b0",
    "4.9",
    "4.9.1",
    "4.9.2"
  ]
}

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