# CVE-2026-81523: Cross-tenant database retargeting via dot/NUL injection in namespace strings in libmongocrypt

> Attackers can manipulate database identifiers to cause incorrect schema selection, leading to limited data disclosure or modification in applications using libmongocrypt.

- **Severity:** Low 2.0 (`CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Aug 2026
- **Updated:** 28 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-81523, UBUNTU-CVE-2026-81523

## What is CVE-2026-81523?

CVE-2026-81523 is a low-severity vulnerability in MongoDB libmongocrypt, published on 27 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A missing input-validation issue in MongoDB libmongocrypt's automatic-encryption context setup allows a caller-supplied database identifier to be accepted without sanitization. The resulting impact is limited to incorrect schema selection, which may lead to limited disclosure or modification of information handled by the application.

Weakness: CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component)

## Which versions are affected by CVE-2026-81523?

It affects 1 product.


Products: Mongodb Libmongocrypt.

## How do I fix CVE-2026-81523?

Apply the vendor's patch.

## Is CVE-2026-81523 being exploited?

There is no known exploitation of CVE-2026-81523 in the wild and no public exploit code.

## Other vulnerabilities in MongoDB libmongocrypt

- [CVE-2026-106433](https://insights.sbomify.com/CVE-2026-106433/): Heap corruption via duplicate masterKey fields in MongoDB libmongocrypt (high 8.7)
- [CVE-2026-84971](https://insights.sbomify.com/CVE-2026-84971/): Persistent client crash loop via undersized FLE2 insert-update ciphertext in decryption path (high 7.1)
- [CVE-2026-84962](https://insights.sbomify.com/CVE-2026-84962/): Authenticated KMS request forgery via CRLF injection in GCP key identifier strings (medium 5.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81523 and fix it if it is affected.

What it is: CVE-2026-81523 is a low-severity vulnerability in MongoDB libmongocrypt, published on 27 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-81523 in the wild and no public exploit code.

Affected product: MongoDB libmongocrypt. 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-2026-81523/ (Markdown: https://insights.sbomify.com/CVE-2026-81523/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81523
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81523
- OSV: https://osv.dev/vulnerability/CVE-2026-81523

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81523/
Summaries are generated and may contain mistakes; the official description above is the record.