GHSA-98QM-WVGF-W4CF
Vulnerability from github – Published: 2026-10-27 15:36 – Updated: 2026-10-27 15:36Impact
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": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 4.18.2"
},
"package": {
"ecosystem": "PyPI",
"name": "pymongo"
},
"ranges": [
{
"events": [
{
"introduced": "3.9.0"
},
{
"fixed": "4.18.3"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-106435"
],
"database_specific": {
"cwe_ids": [
"CWE-125"
],
"github_reviewed": true,
"github_reviewed_at": "2026-10-27T15:36:35Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "### Impact\nThe C extension\u0027s BSON decoder scans a Regex element\u0027s pattern and flags strings with strlen before checking the document\u0027s remaining length, so a crafted truncated Regex element can read past the end of the caller\u0027s 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 \u2014 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\u0027s own transport and pure-Python installs are not affected. All releases through 4.18.2 are affected when the C extension is loaded.\n\n### Patches\nFixed in PyMongo 4.18.3. Malformed Regex elements now raise InvalidBSON on every accepted buffer type; valid documents decode unchanged.\n\n### Workarounds\nDecode untrusted BSON only from NUL-terminated buffers \u2014 bytes or bytearray \u2014 and copy mmap input first, e.g. bytes(mm[:size]).",
"id": "GHSA-98qm-wvgf-w4cf",
"modified": "2026-10-27T15:36:36Z",
"published": "2026-10-27T15:36:35Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/mongodb/mongo-python-driver/security/advisories/GHSA-98qm-wvgf-w4cf"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-106435"
},
{
"type": "WEB",
"url": "https://github.com/mongodb/mongo-python-driver/pull/3109"
},
{
"type": "WEB",
"url": "https://github.com/mongodb/mongo-python-driver/commit/bb8d4e195275e75bd94ebeffb53cc747d357fcf4"
},
{
"type": "PACKAGE",
"url": "https://github.com/mongodb/mongo-python-driver"
},
{
"type": "WEB",
"url": "https://github.com/mongodb/mongo-python-driver/releases/tag/4.18.3"
},
{
"type": "WEB",
"url": "https://jira.mongodb.org/browse/PYTHON-6110"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "MongoDB Python Driver: Out-of-bounds read in BSON decoding via a malformed Regex element"
}
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