CVE-2026-84971
Persistent client crash loop via undersized FLE2 insert-update ciphertext in decryption path
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.
INFO
Published Date :
Sept. 3, 2026, 3:17 p.m.
Last Modified :
Sept. 17, 2026, 1:59 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | a39b4221-9bd0-4244-95fc-f3e2e07f1deb | ||||
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 4.0 | HIGH | a39b4221-9bd0-4244-95fc-f3e2e07f1deb | ||||
| CVSS 4.0 | HIGH | [email protected] |
Solution
- Validate input size before decryption.
- Implement robust error handling.
- Update the encryption library.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-84971.
| URL | Resource |
|---|---|
| https://jira.mongodb.org/browse/MONGOCRYPT-971 | Vendor Advisory Issue Tracking Patch |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-84971 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-84971
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-84971 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-84971 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Sep. 17, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:mongodb:libmongocrypt:*:*:*:*:*:*:*:* versions from (including) 1.7.0 up to (excluding) 1.20.4 Added Reference Type MongoDB, Inc.: https://jira.mongodb.org/browse/MONGOCRYPT-971 Types: Issue Tracking, Patch, Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Sep. 03, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-84971', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-09-03T15:10:07.983007Z'} -
New CVE Received by [email protected]
Sep. 03, 2026
Action Type Old Value New Value Added 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. Added CVSS V4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CVSS V3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Added CWE CWE-617 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/84xxx/CVE-2026-84971.json">CVE-2026-84971</a> Added Reference https://jira.mongodb.org/browse/MONGOCRYPT-971