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CVE-2026-84969— Heap overflow via truncated base64 encoding of binary fields in length-limited JSON output

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 转 JSON 的辅助函数存在内存处理错误：当编码二进制字段且输出被调用方配置的长度上限截断时，可能会在堆缓冲区的末尾之后写入少量字节。能够控制文档内容但对该驱动所在应用没有特权的一方，可能会导致预期缓冲区之外的少量数据被修改。

CVSS 3.7 · Low

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 2

VendorProduct Version RangeStatus
MongoDB C Driver 1.30.0< 1.30.9 affected
2.0.0< 2.5.2 affected
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I. Basic Information for CVE-2026-84969

Vulnerability Information
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Vulnerability Title
Heap overflow via truncated base64 encoding of binary fields in length-limited JSON output
Source: CVE Program / CVE List V5
Vulnerability Description
A memory-handling error in the BSON-to-JSON conversion helpers of the MongoDB C Driver can write a small number of bytes past the end of a heap buffer when a binary field is encoded and the output is cut short at a caller-configured length limit. A party who supplies the document content, with no privileges on the application that links the driver, may cause a small amount of data outside the intended buffer to be altered.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存写
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
MongoDB C Driver 1.30.0 ~ 1.30.9 -

II. Public POCs for CVE-2026-84969

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III. Intelligence Information for CVE-2026-84969

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Vendor Pages for CVE-2026-84969 (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-2026-84966 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

IV. Related Vulnerabilities

Same product: C Driver
Same vendor: MongoDB
Same weakness: CWE-787

V. Comments for CVE-2026-84969

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