# CVE-2026-81527 — MongoDB C# Driver

> As of 2026-08-28, CVE-2026-81527 is a MEDIUM-severity vulnerability in MongoDB C# Driver, CVSS v3.1 6.5, EPSS 0.1% (7.9th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-81527 as of 2026-08-28; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-08-28

## What is CVE-2026-81527?

A NoSQL/expression injection weakness exists in the LINQ-to-aggregation query translation layer of the MongoDB C# Driver, in both aggregation expression and query filter translation. When application-supplied values are embedded in certain query constructs, special elements contained within those values are not properly escaped before the resulting query is transmitted to the database, so portions of the value may be interpreted by the database as query logic rather than as data. A user able to supply values that an application incorporates into an affected query may thereby cause unintended data to be returned or query results to be altered.

The record classifies CVE-2026-81527 under weakness class [CWE-943](https://cwe.mitre.org/data/definitions/943.html). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 39 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 6.5 — MEDIUM (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N`)
- **CVSS v4.0 base score:** 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **EPSS (FIRST):** 0.1% probability of exploitation in the next 30 days, higher than 7.9% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 3.6/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-08-27, last modified 2026-08-28

## Is CVE-2026-81527 being exploited?

It currently carries a trending score of 31 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [MongoDB](https://intel.threadlinqs.com/vendors/mongodb): C# Driver

## How to fix CVE-2026-81527

No vendor patch reference has been recorded for CVE-2026-81527 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-81527

No threat campaign in the Threadlinqs corpus currently references CVE-2026-81527, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, FIRST EPSS. Last verified by Threadlinqs on 2026-08-30. This product uses the NVD API but is not endorsed or certified by the NVD.

**Other references**

- [jira.mongodb.org](https://jira.mongodb.org/browse/CSHARP-6156)
- [nuget.org](https://www.nuget.org/packages/MongoDB.Driver/3.11.1)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-81527
Full detection coverage and IOCs for threats exploiting CVE-2026-81527 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp