CVE-2026-84971Network attack vectorHinoki check available

Client process termination via undersized FLE2 ciphertext

Published Sep 3, 2026 · Updated Sep 3, 2026

Reachable assertion in MongoDB libmongocrypt 1.7.0 through 1.20.3 allows remote authenticated users to terminate client processes. The FLE2 insert-update decryption path accepts an undersized ciphertext value and reaches an internal length assertion instead of rejecting the malformed input. The attacker must place the value where an application decrypts it or control a response the application receives; the resulting abort interrupts only that process, but repeated input can sustain a crash loop.

CVSS severity7.1
High
EPSS probability0.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Reachable assertion in MongoDB libmongocrypt 1.7.0 through 1.20.3 allows remote authenticated users to terminate client processes. The FLE2 insert-update decryption path accepts an undersized ciphertext value and reaches an internal length assertion instead of rejecting the malformed input. The attacker must place the value where an application decrypts it or control a response the application receives; the resulting abort interrupts only that process, but repeated input can sustain a crash loop.

The record

CVE
CVE-2026-84971
Published
Sep 3, 2026
Updated
Sep 3, 2026
Vendor
MongoDB
Product
libmongocrypt
Classifications
CWE-617, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 3, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.7.0 <1.20.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

MongoDB · libmongocryptversion=1.7.0 <1.20.4

Published CVSS scores

7.1MongoDB CNACVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
6.5MongoDB CNACVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-617Reachable Assertion
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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