CVE-2026-84971— Persistent client crash loop via undersized FLE2 insert-update ciphertext in decryption path
Quick assessment
Affected
MongoDB libmongocrypt
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 libmongocrypt是美国MongoDB公司开源的一个加密操作库。 MongoDB libmongocrypt 1.7.0版本至1.20.4之前版本存在异常处理不当漏洞，该漏洞源于解密路径中对意外值大小处理不当，导致内部检查失败，可能使使用该库的应用程序停止运行。
Possible ATT&CK Techniques 1 AI
T1190 · Exploit Public-Facing ApplicationAffected Version Matrix 1
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| MongoDB | libmongocrypt | 1.7.0< 1.20.4 |
affected |
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I. Basic Information for CVE-2026-84971
Vulnerability Information
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Vulnerability Title
Persistent client crash loop via undersized FLE2 insert-update ciphertext in decryption path
Source: CVE Program / CVE List V5
Vulnerability Description
Improper handling of an unexpected value size in the decryption path of a client-side encryption library can cause a failed internal check that terminates the process using the library. A party able to place a suitably formed encrypted value where an application will decrypt it, or able to control the responses the application receives, may cause that application to stop running.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
可达断言
Source: CVE Program / CVE List V5
Vulnerability Title
MongoDB libmongocrypt 异常处理不当漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
MongoDB libmongocrypt是美国MongoDB公司开源的一个加密操作库。 MongoDB libmongocrypt 1.7.0版本至1.20.4之前版本存在异常处理不当漏洞，该漏洞源于解密路径中对意外值大小处理不当，导致内部检查失败，可能使使用该库的应用程序停止运行。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| MongoDB | libmongocrypt | 1.7.0 ~ 1.20.4 | - |
|
II. Public POCs for CVE-2026-84971
| # | POC Description | Source Link | Shenlong Link |
|---|
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Vendor Pages for CVE-2026-84971 (1)
Same Patch Batch · MongoDB · 2026-09-03 · 10 CVEs total
| 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 |
| CVE-2026-84969 | 3.7 LOW | Heap overflow via truncated base64 encoding of binary fields in length-limited JSON output |
IV. Related Vulnerabilities
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V. Comments for CVE-2026-84971
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