# CVE-2026-81529: Connection-option injection via unescaped settings in the canonical MongoDB URL builder

> Attackers can inject connection options via unescaped text in the MongoDB C# Driver URL builder, potentially altering security settings.

- **Severity:** High 7.1 (`CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:H/VI:L/VA:N/SC:H/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 27 Aug 2026
- **Updated:** 28 Aug 2026

## What is CVE-2026-81529?

CVE-2026-81529 is a high-severity vulnerability in MongoDB C# Driver, published on 27 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Improper neutralization of delimiters in connection-URL construction allows connection-option injection in the MongoDB C# Driver. When an application passes untrusted text into the driver's connection-URL builder and round-trips the builder back into a client configuration, the untrusted text is serialized without neutralizing the URL/option delimiters and is then re-parsed as authoritative connection options. A low-privileged user of such an application can thereby introduce or suppress security-relevant connection settings.

Weakness: CWE-88 (Improper Neutralization of Argument Delimiters in a Command)

## Which versions are affected by CVE-2026-81529?

It affects 1 product.


Products: Mongodb C\# Driver.

## How do I fix CVE-2026-81529?

No fix has been published for CVE-2026-81529 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-81529 being exploited?

There is no known exploitation of CVE-2026-81529 in the wild and no public exploit code.

## Other vulnerabilities in MongoDB C# Driver

- [CVE-2026-88026](https://insights.sbomify.com/CVE-2026-88026/): Regular expression injection via unescaped characters in LINQ query translation in MongoDB C# Driver (high 7.1)
- [CVE-2026-81527](https://insights.sbomify.com/CVE-2026-81527/): NoSQL injection via unquoted constant GroupBy keys in LINQ pipeline translation (medium 6.9)
- [CVE-2026-81530](https://insights.sbomify.com/CVE-2026-81530/): KMS master key exposure via unredacted credential serialization in driver settings string (medium 6.8)
- [CVE-2022-48282](https://insights.sbomify.com/CVE-2022-48282/): Deserializing compromised object with MongoDB .NET/C# Driver may cause remote code execution (medium 6.6)
- [CVE-2026-88025](https://insights.sbomify.com/CVE-2026-88025/): GridFS data disclosure and deletion via query-operator injection in file IDs in the MongoDB C# Driver (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81529 and fix it if it is affected.

What it is: CVE-2026-81529 is a high-severity vulnerability in MongoDB C# Driver, published on 27 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-81529 in the wild and no public exploit code.

Affected product: MongoDB C# Driver. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-81529/ (Markdown: https://insights.sbomify.com/CVE-2026-81529/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81529
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81529
- OSV: https://osv.dev/vulnerability/CVE-2026-81529

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81529/
Summaries are generated and may contain mistakes; the official description above is the record.