# CVE-2026-5246: Cesanta Mongoose P-384 Public Key mongoose.c mg_tls_verify_cert_signature authorization

> Remote attackers can bypass authorization in Cesanta Mongoose via manipulated P-384 public key signatures, requiring complex exploitation techniques.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/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:** 2 Apr 2026
- **Updated:** 2 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-5246, GHSA-hm7q-jq63-pr78, JLSEC-2026-371, UBUNTU-CVE-2026-5246

## What is CVE-2026-5246?

CVE-2026-5246 is a medium-severity authentication bypass vulnerability in Cesanta Mongoose, published on 2 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability was determined in Cesanta Mongoose up to 7.20. Affected is the function mg_tls_verify_cert_signature of the file mongoose.c of the component P-384 Public Key Handler. Executing a manipulation can lead to authorization bypass. The attack can be executed remotely. Attacks of this nature are highly complex. The exploitability is told to be difficult. The exploit has been publicly disclosed and may be utilized. Upgrading to version 7.21 is able to address this issue. This patch is called 0d882f1b43ff2308b7486a56a9d60cd6dba8a3f1. The affected component should be upgraded. The vendor was contacted early, responded in a very professional manner and quickly released a fixed version of the affected product.

Weakness: CWE-639 (Authorization Bypass Through User-Controlled Key), CWE-285 (Improper Authorization)

## Which versions are affected by CVE-2026-5246?

It affects 1 product.


Products: Cesanta Mongoose.

## How do I fix CVE-2026-5246?

Upgrade to a fixed version.

## Is CVE-2026-5246 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-5246 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-2026-5246 and fix it if it is affected.

What it is: CVE-2026-5246 is a medium-severity authentication bypass vulnerability in Cesanta Mongoose, published on 2 Apr 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-2026-5246 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-2026-5246/ (Markdown: https://insights.sbomify.com/CVE-2026-5246/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-5246
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-5246
- OSV: https://osv.dev/vulnerability/CVE-2026-5246

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-5246/
Summaries are generated and may contain mistakes; the official description above is the record.