# CVE-2026-81528 — MongoDB C# Driver

> As of 2026-08-28, CVE-2026-81528 is a MEDIUM-severity vulnerability in MongoDB C# Driver, CVSS v3.1 5.4, EPSS 0.1% (5.8th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-81528 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-2026-81528?

A MongoDB C# driver document-replacement code path omits the element-name/shape validation that the equivalent write paths apply, so a value supplied as a replacement is forwarded to the server without neutralization of query-language special elements. An application that passes untrusted, loosely-typed input as a replacement value therefore allows that input to be interpreted by the database as update logic rather than as data, executing under the application's own database credentials. Applications using strongly-typed document mappings are not affected.

The record classifies CVE-2026-81528 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 low-privilege credentials, 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:** 5.4 — MEDIUM (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N`)
- **CVSS v4.0 base score:** 5.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/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 5.8% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4.9/10 — 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-2026-81528 being exploited?

Weaponised exploit code for CVE-2026-81528 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. It currently carries a trending score of 39 in the Threadlinqs vulnerability feed.

- [trickest/cve](https://github.com/trickest/cve/blob/main/2026/CVE-2026-81528.md) (trickest)

## Affected products and versions

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

## How to fix CVE-2026-81528

No vendor patch reference has been recorded for CVE-2026-81528 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-2026-81528

No threat campaign in the Threadlinqs corpus currently references CVE-2026-81528, 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, GitHub Security Advisories, public proof-of-concept repositories. 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-6158)
- [nuget.org](https://www.nuget.org/packages/MongoDB.Driver/3.11.1)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-81528
Full detection coverage and IOCs for threats exploiting CVE-2026-81528 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp