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CVE-2026-84970— Heap over-read or silent misparse via 32-bit truncation of JSON length in BSON JSON parser

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++ 驱动的 BSON 库中的 JSON 解析组件存在数值截断缺陷。若攻击者能够控制嵌入式应用传递给库的公共 JSON 解析接口的文本内容，且该文本非常大时，可能导致库读取超出所提供缓冲区的内存并返回给调用者、静默地仅将输入的一部分作为完整文档接受，或导致进程终止。此问题无需 MongoDB 服务器、凭据或非默认配置即可触发；其影响范围仅限于使用该库的进程。

CVSS 6.2 · Medium

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

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-2026-84970

Vulnerability Information
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Vulnerability Title
Heap over-read or silent misparse via 32-bit truncation of JSON length in BSON JSON parser
Source: CVE Program / CVE List V5
Vulnerability Description
A numeric truncation weakness exists in the JSON parsing component of the MongoDB C++ Driver's BSON library. An actor who controls the text that an embedding application hands to the library's public JSON parsing interface, when that text is very large, can cause the library to read memory beyond the supplied buffer and return it to the caller, to silently accept only part of the input as a complete document, or to terminate the process. No MongoDB server, credentials, or non-default configuration is required; the effect is confined to the process that uses the library.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/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-2026-84970

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III. Intelligence Information for CVE-2026-84970

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Other References for CVE-2026-84970 (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-2026-84964 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-2026-84966 5.1 MEDIUM BSON element injection via NUL-embedded document keys in builder append
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-2026-84970

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