Medium severity · published Sep 3, 2026
CVE-2026-84971
Persistent client crash loop via undersized FLE2 insert-update ciphertext in decryption path
6.5
CVSS
0.3%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 18% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MO
MongoDB · MongoDB
1.7.0 before 1.20.4 · source: vendor
LI
Libmongocrypt · Mongodb
1.7.0 before 1.20.4 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-84971
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-84971
Vendor Advisory
https://jira.mongodb.org/browse/MONGOCRYPT-971
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