A fourth party is a supplier that one of your own vendors depends on. If the buyer is the first party, you are the second, your vendors are the third, and their suppliers are the fourth. Buyers ask because a failure deep in the chain can still reach their data.
The chain in plain terms
Say a buyer uses your SaaS. You host on a cloud provider, send email through a messaging service, and take payments through a processor. Those are your vendors. The cloud provider has its own data center operators and hardware suppliers. Those are fourth parties from the buyer's view.
For software, the same idea applies in a different shape. Your product includes open source packages. Those packages depend on other packages maintained by people you have never met. That tree is a fourth party and beyond, in practice.
Why enterprise buyers care
Large companies run third party risk programs. They are responsible for the vendors they pick, and many are asked by their own regulators or customers how they oversee deeper layers. A startup rarely gets asked to list every supplier of every supplier. The typical request is narrower: which of your vendors handle our data, and how do you oversee them?
What a startup can reasonably know
| Layer | What you can state |
|---|---|
| Your vendors (third parties) | Name, purpose, what data they touch, location, contract in place |
| Their critical suppliers (fourth parties) | What the vendor publishes: subprocessor lists, trust pages, reports |
| Open source dependencies | Your SBOM, including transitive packages |
You cannot audit your cloud provider's suppliers. You can read what they publish, and you can say that you do.
A practical process
- Build a vendor register with one row per vendor and the data each handles.
- For each critical vendor, record where their subprocessor list and security documentation live.
- Set a review date for each, at least annually.
- For software, keep SBOMs per release so you can answer "does your product include package X" quickly.
- Subscribe to vendor incident notices and note who reads them.
See also the related guide on fourth party risk mapping and the vendor register checklist.
Wording the answer
"We maintain a register of vendors that process customer data and review their published security documentation and subprocessor lists annually. For software components we keep an SBOM per release that includes transitive dependencies. We do not audit the suppliers of our vendors directly."
That last sentence matters. Reviewers appreciate a clear boundary more than an inflated claim.
Common mistakes
- Listing only paid vendors and forgetting free developer tools that touch code.
- Treating the SBOM as complete when it only covers one repository.
- Saying "we monitor all fourth parties," which is almost never true.
Inventory also needs an owner. Without one, the register ages out in a quarter.
Try it yourself
Click through it at your own pace, or open it full screen. Note how deep the dependency tree goes beyond the packages you chose directly, which is the software version of the fourth party question.
Safeguard produces dependency inventory and SBOMs, and can help with asset discovery for the tools your team uses. A free scan shows the software side.
Quick check
Do I have to list my cloud provider's suppliers?
Usually no. Point to the provider's published subprocessor list and security documentation, and say you review them.
Is an open source maintainer a fourth party?
In supply chain terms the packages are components in your software. Buyers mostly care that you can inventory and respond to them.
Last reviewed: 19 October 2026.
