# CVE-2026-103503: Hex trusts its bundled CA certificates when cacerts_path is set

> Attackers can bypass certificate validation in Hex when a custom CA path is configured, allowing host impersonation via bundled CA trust.

- **Severity:** Medium 5.9 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:A/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 12 Oct 2026
- **Updated:** 16 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-103503, EEF-CVE-2026-103503, GHSA-rw8q-hg7m-cxgr, UBUNTU-CVE-2026-103503

## What is CVE-2026-103503?

CVE-2026-103503 is a medium-severity vulnerability in hexpm hex, published on 12 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Improper Certificate Validation vulnerability in hexpm hex allows an attacker who can intercept HTTPS connections, and holds a certificate for a Hex host issued by a CA in Hex's bundled CA store, to impersonate that host to users who set cacerts_path to a CA store that leaves that CA out.

cacerts_path (HEX_CACERTS_PATH) is documented as the path to the CA certificate store, used instead of the CA bundle that ships with Hex. Hex.HTTP.SSL.ssl_opts/1 passes the configured store as the cacerts option, but builds the partial_chain callback from the bundled store whether cacerts_path is set or not. Hex.HTTP.SSL.partial_chain/2 accepts a server chain when any certificate in it has the same public key as a bundled CA certificate, so a chain that leads to a bundled CA passes verification although the configured store doesn't contain that CA. Hostname verification still applies.

This issue affects hex: from 0.20.2 before 2.5.2.

Weakness: CWE-295 (Improper Certificate Validation)

## Which versions are affected by CVE-2026-103503?


## How do I fix CVE-2026-103503?

Upgrade to a fixed version.

## Is CVE-2026-103503 being exploited?

There is no known exploitation of CVE-2026-103503 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-103503 and fix it if it is affected.

What it is: CVE-2026-103503 is a medium-severity vulnerability in hexpm hex, published on 12 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-103503 in the wild and no public exploit code.

Affected product: hexpm hex. 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-2026-103503/ (Markdown: https://insights.sbomify.com/CVE-2026-103503/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-103503
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-103503
- OSV: https://osv.dev/vulnerability/CVE-2026-103503

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-103503/
Summaries are generated and may contain mistakes; the official description above is the record.