# CVE-2026-2966: Cesanta Mongoose DNS Transaction ID dns.c mg_sendnsreq random values

> Insufficiently random DNS transaction IDs in Cesanta Mongoose allow remote attackers to potentially bypass security checks via complex attacks.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Feb 2026
- **Updated:** 23 Feb 2026
- **Also known as:** DEBIAN-CVE-2026-2966, GHSA-m5mm-h952-fxjj, JLSEC-2026-366, UBUNTU-CVE-2026-2966

## What is CVE-2026-2966?

CVE-2026-2966 is a medium-severity vulnerability in Cesanta Mongoose, published on 23 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A weakness has been identified in Cesanta Mongoose up to 7.20. The impacted element is the function mg_sendnsreq of the file /src/dns.c of the component DNS Transaction ID Handler. Executing a manipulation of the argument random can lead to insufficiently random values. The attack can be launched remotely. The attack requires a high level of complexity. The exploitability is regarded as difficult. The exploit has been made available to the public and could be used for attacks. The vendor was contacted early about this disclosure but did not respond in any way.

Weakness: CWE-330 (Use of Insufficiently Random Values), CWE-310

## Which versions are affected by CVE-2026-2966?

It affects 1 product.


Products: Cesanta Mongoose.

## How do I fix CVE-2026-2966?

No fix published yet.

## Is CVE-2026-2966 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-2966 exists.

## Other vulnerabilities in Cesanta Mongoose

- [CVE-2022-25299](https://insights.sbomify.com/CVE-2022-25299/): Arbitrary File Write (critical 9.8)
- [CVE-2020-25756](https://insights.sbomify.com/CVE-2020-25756/): Memory corruption in n/a (critical 9.8)
- [CVE-2019-19307](https://insights.sbomify.com/CVE-2019-19307/): Integer overflow in n/a (critical 9.8)
- [CVE-2019-12951](https://insights.sbomify.com/CVE-2019-12951/): Memory corruption in n/a (critical 9.8)
- [CVE-2018-20353](https://insights.sbomify.com/CVE-2018-20353/): Use after free in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-2966 and fix it if it is affected.

What it is: CVE-2026-2966 is a medium-severity vulnerability in Cesanta Mongoose, published on 23 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-2966 exists.

Affected product: Cesanta Mongoose. 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-2026-2966/ (Markdown: https://insights.sbomify.com/CVE-2026-2966/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-2966
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-2966
- OSV: https://osv.dev/vulnerability/CVE-2026-2966

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-2966/
Summaries are generated and may contain mistakes; the official description above is the record.