Persistent client crash loop via undersized FLE2 insert-update ciphertext in decryption path (CVE-2026-84971) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-84971

Persistent client crash loop via undersized FLE2 insert-update ciphertext in decryption path

Answer in brief

CVE-2026-84971 records a Unknown severity vulnerability in Persistent client crash loop via undersized FLE2 insert-update ciphertext in decryption path. The current sources do not mark it as known exploited. The current feed maps MongoDB/libmongocrypt (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 3, 2026Updated Sep 3, 2026Source checked Sep 3, 2026First seen by HOL Sep 3, 2026Material review Sep 3, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps MongoDB/libmongocrypt (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
MongoDB/libmongocryptgeneric	>=1.7.0 <1.20.4	1.20.4

Recommended response

Check inventory. Check lockfiles and deployed manifests for MongoDB/libmongocrypt.
Review the reported fix. Update MongoDB/libmongocrypt to 1.20.4 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 3, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 3, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 3, 2026

Sources and claim methodology

Source referencejira.mongodb.org

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.