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CVE-2026-84965— Heap write primitive via size round-up wrap during JSON parsing on 32-bit builds

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.

BSON 库的 JSON 解析代码中存在整数回绕（integer wraparound）漏洞，发生在分配大小的计算过程中。这可能导致缓冲区在后续的拷贝操作仍通过陈旧指针进行写入时已被释放。在采用 32 位大小字的构建版本中，能够向链接该库的应用程序提供足够大的 JSON 输入的未认证攻击者，可能触发该应用程序意外终止，从而导致拒绝服务（Denial of Service）。

CVSS 5.1 · Medium

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 2

VendorProduct Version RangeStatus
MongoDB C Driver 1.10.0< 1.30.9 affected
2.0.0< 2.5.2 affected
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I. Basic Information for CVE-2026-84965

Vulnerability Information
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Vulnerability Title
Heap write primitive via size round-up wrap during JSON parsing on 32-bit builds
Source: CVE Program / CVE List V5
Vulnerability Description
An integer wraparound in an allocation size calculation in the BSON library's JSON parsing code can cause a buffer to be released while a following copy operation still writes through the stale pointer. On builds where sizes are 32 bits, an unauthenticated party able to supply a sufficiently large JSON input to an application that links the library may cause that application to terminate unexpectedly, resulting in denial of service.
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
整数溢出或超界折返
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
MongoDB C Driver 1.10.0 ~ 1.30.9 -

II. Public POCs for CVE-2026-84965

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III. Intelligence Information for CVE-2026-84965

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Vendor Pages for CVE-2026-84965 (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-2026-84966 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-190

V. Comments for CVE-2026-84965

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