# CVE-2026-2967: Cesanta Mongoose TCP Sequence Number net_builtin.c getpeer verification of source

> An attacker can bypass source verification in Cesanta Mongoose's TCP sequence number handler, potentially spoofing communication channels.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/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-2026-2967, GHSA-c6h3-vh8h-r8mj, JLSEC-2026-367, UBUNTU-CVE-2026-2967

## What is CVE-2026-2967?

CVE-2026-2967 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 security vulnerability has been detected in Cesanta Mongoose up to 7.20. This affects the function getpeer of the file /src/net_builtin.c of the component TCP Sequence Number Handler. The manipulation leads to improper verification of source of a communication channel. The attack may be initiated remotely. The attack's complexity is rated as high. The exploitability is reported as difficult. The exploit has been disclosed publicly and may be used. The vendor was contacted early about this disclosure but did not respond in any way.

Weakness: CWE-940 (Improper Verification of Source of a Communication Channel)

## Which versions are affected by CVE-2026-2967?

It affects 1 product.


Products: Cesanta Mongoose.

## How do I fix CVE-2026-2967?

No fix published yet.

## Is CVE-2026-2967 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-2967 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-2026-2967 and fix it if it is affected.

What it is: CVE-2026-2967 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-2026-2967 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-2026-2967/ (Markdown: https://insights.sbomify.com/CVE-2026-2967/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-2967
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-2967
- OSV: https://osv.dev/vulnerability/CVE-2026-2967

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-2967/
Summaries are generated and may contain mistakes; the official description above is the record.