# CVE-2026-8406: openSIS Classic 9.3 - Insecure Direct Object Reference in Sent Mail

> Authenticated users can read other users' sent messages by manipulating the mail_id parameter in the messaging module.

- **Severity:** High 7.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 11 Jun 2026
- **Updated:** 11 Jun 2026
- **Also known as:** GHSA-vgf3-fpxc-h968

## What is CVE-2026-8406?

CVE-2026-8406 is a high-severity missing authorization vulnerability in OS4ED openSIS-Classic, published on 11 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

openSIS Classic 9.3 contains an insecure direct object reference vulnerability in the messaging module. Any authenticated user with access to the messaging module can request sent-message details from modules/messaging/SentMail.php by supplying an arbitrary mail_id value.

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

## Which versions are affected by CVE-2026-8406?


## How do I fix CVE-2026-8406?

No fix has been published for CVE-2026-8406 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-8406 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-8406 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-8406 and fix it if it is affected.

What it is: CVE-2026-8406 is a high-severity missing authorization vulnerability in OS4ED openSIS-Classic, published on 11 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-8406 exists.

Affected product: OS4ED openSIS-Classic. 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-2026-8406/ (Markdown: https://insights.sbomify.com/CVE-2026-8406/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-8406
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-8406
- OSV: https://osv.dev/vulnerability/CVE-2026-8406

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-8406/
Summaries are generated and may contain mistakes; the official description above is the record.