# CVE-2026-53903: Insecure Direct Object Reference in MCO

> Attackers can access other users' trading documents by guessing IDs due to missing authorization checks in the MCO web application.

- **Severity:** Medium 5.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/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:** 1 Jul 2026
- **Updated:** 1 Jul 2026
- **Also known as:** GHSA-h63w-8j45-g3cx

## What is CVE-2026-53903?

CVE-2026-53903 is a medium-severity missing authorization vulnerability in MyComplianceOffice MCO, published on 1 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

MCO is vulnerable to an Insecure Direct Object Reference (IDOR) vulnerability in the /customer/servlet/mco/webapi/trading-document/fetchPdfStatement endpoint. The application does not properly validate whether an authenticated user is authorized to access a requested document, allowing direct retrieval based on a user-supplied identifier.
An attacker can access trading documents belonging to other users by providing a valid document ID. Although exploitation requires guessing the identifier, predictable ID patterns enable feasible enumeration, leading to unauthorized disclosure of sensitive information.

Because vendor contact attempts were unsuccessful, the vulnerability has only been confirmed in version 25.3.3.1 but may also affect other versions.

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

## Which versions are affected by CVE-2026-53903?

It affects 1 product.


Products: Mycomplianceoffice Mycomplianceoffice.

## How do I fix CVE-2026-53903?

No fix has been published for CVE-2026-53903 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-53903 being exploited?

There is no known exploitation of CVE-2026-53903 in the wild and no public exploit code.

## Other vulnerabilities in MyComplianceOffice MCO

- [CVE-2026-53902](https://insights.sbomify.com/CVE-2026-53902/): Privilege Escalation in MCO (high 7.1)
- [CVE-2026-53908](https://insights.sbomify.com/CVE-2026-53908/): User Enumeration in MCO (medium 6.9)
- [CVE-2026-53905](https://insights.sbomify.com/CVE-2026-53905/): Unauthorized Access to Administrator ACL View in MCO (medium 5.3)
- [CVE-2026-53909](https://insights.sbomify.com/CVE-2026-53909/): Arbitrary File Upload in MCO (medium 5.3)
- [CVE-2026-53906](https://insights.sbomify.com/CVE-2026-53906/): Path Disclosure and Path Traversal in MCO (medium 5.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-53903 and fix it if it is affected.

What it is: CVE-2026-53903 is a medium-severity missing authorization vulnerability in MyComplianceOffice MCO, published on 1 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-53903 in the wild and no public exploit code.

Affected product: MyComplianceOffice MCO. 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-2026-53903/ (Markdown: https://insights.sbomify.com/CVE-2026-53903/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53903
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53903
- OSV: https://osv.dev/vulnerability/CVE-2026-53903

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53903/
Summaries are generated and may contain mistakes; the official description above is the record.