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CVE-2026-84966— BSON element injection via NUL-embedded document keys in builder append

Quick assessment

Affected
MongoDB C++ Driver
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

MongoDB C++ 驱动中 BSON 文档构建组件存在不正确的数值类型转换问题，这可能导致长度值被错误解释。当应用程序向构建器传入一个极长的、未终止的字段名时，库可能会读取预期缓冲区之外的内存，从而导致调用进程终止。该漏洞无需身份验证，但调用应用程序必须以特定形式传入过长的名称才能触发此问题。

CVSS 5.1 · Medium

Possible ATT&CK Techniques 1 AI

T1203 · Exploitation for Client Execution

Affected Version Matrix 1

VendorProduct Version RangeStatus
MongoDB C++ Driver 3.2.0< 4.5.2 affected
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I. Basic Information for CVE-2026-84966

Vulnerability Information
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Vulnerability Title
BSON element injection via NUL-embedded document keys in builder append
Source: CVE Program / CVE List V5
Vulnerability Description
An incorrect numeric type conversion in the BSON document building component of the MongoDB C++ Driver may cause a length value to be interpreted incorrectly. When an application supplies an extremely large, non-terminated field name to the builder, the library may read memory outside the intended buffer and terminate the calling process. No authentication is required, but the calling application must pass the oversized name in a specific form.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
数值类型间的不正确转换
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
MongoDB C++ Driver 3.2.0 ~ 4.5.2 -

II. Public POCs for CVE-2026-84966

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III. Intelligence Information for CVE-2026-84966

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Vendor Pages for CVE-2026-84966 (1)

Same Patch Batch · MongoDB · 2026-09-03 · 10 CVEs total

CVE-2026-84971 6.5 MEDIUM Persistent client crash loop via undersized FLE2 insert-update ciphertext in decryption pa
CVE-2026-84970 6.2 MEDIUM Heap over-read or silent misparse via 32-bit truncation of JSON length in BSON JSON parser
CVE-2026-84964 5.9 MEDIUM Heap corruption via OCSP request double free from crafted multi-URL certificate in TLS cli
CVE-2026-84963 5.3 MEDIUM Silent field truncation via unchecked int cast of huge JSON string values in JSON-to-BSON
CVE-2026-84968 5.3 MEDIUM Heap out-of-bounds read via corrupt nested BSON in field path error message
CVE-2026-84965 5.1 MEDIUM Heap write primitive via size round-up wrap during JSON parsing on 32-bit builds
CVE-2026-84967 4.3 MEDIUM Arbitrary command execution via shell-expanded connection string in Launch MongoDB Shell t
CVE-2026-84962 4.2 MEDIUM Authenticated KMS request forgery via CRLF injection in GCP key identifier strings
CVE-2026-84969 3.7 LOW Heap overflow via truncated base64 encoding of binary fields in length-limited JSON output

IV. Related Vulnerabilities

Same product: C++ Driver
Same vendor: MongoDB
Same weakness: CWE-681

V. Comments for CVE-2026-84966

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