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CVE-2026-84963— Silent field truncation via unchecked int cast of huge JSON string values in JSON-to-BSON 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 驱动中 BSON 库的 JSON 解析组件存在数值转换错误，可能导致异常大的文本值被静默截短，或对应字段被直接忽略，而解析操作仍会报告成功且不返回任何错误。能够向使用该组件的应用程序提供输入数据的未认证方，可能会导致应用程序存储的数据与提交的数据不一致，从而引发非预期的数据篡改。

CVSS 5.3 · Medium

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-2026-84963

Vulnerability Information
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Vulnerability Title
Silent field truncation via unchecked int cast of huge JSON string values in JSON-to-BSON parser
Source: CVE Program / CVE List V5
Vulnerability Description
An incorrect numeric conversion in the JSON parsing component of the MongoDB C Driver's BSON library may cause an unusually large text value to be silently shortened, or the corresponding field to be omitted, while the parsing operation still reports success and returns no error. An unauthenticated party who can supply the input processed by an application that uses this component may cause that application to hold data that does not match what was submitted, which may result in unintended alteration of data.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
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 1.10.0 ~ 1.30.9 -

II. Public POCs for CVE-2026-84963

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III. Intelligence Information for CVE-2026-84963

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Other References for CVE-2026-84963 (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-2026-84968 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-2026-84963

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