# GHSA-9r75-g2cr-3h76: Vercel Workflow Allows Webhook Creation with Predictable User-Specified Tokens

> Unauthenticated attackers can guess predictable webhook tokens to inject payloads and trigger unauthorized workflow side effects.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Mar 2026

## What is GHSA-9r75-g2cr-3h76?

GHSA-9r75-g2cr-3h76 is an authentication bypass vulnerability in @workflow/core, published on 6 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

`createWebhook()` in Vercel Workflow DevKit accepts a user-specified `token` parameter that serves as the credential for the public webhook endpoint `/.well-known/workflow/v1/webhook/{token}`. Official documentation recommended predictable token patterns, making it possible for an unauthenticated remote attacker to guess the token and inject arbitrary payloads into the workflow execution context.

#### Impact

An attacker who guesses a webhook token can resume the associated workflow with an attacker-controlled HTTP request body, potentially triggering downstream side effects such as API calls, database writes, or deployments.

#### Fix

* Upgrade to version 4.2.0-beta.64. The fix removes the `token` option from `createWebhook()` so that webhook tokens are always randomly generated by the SDK.
* Runs created with versions prior to 4.2.0-beta.64, that are 1) still active (i.e. running), and 2) have open hooks, are still susceptible to this vulnerability. If users suspect the hook tokens are predictable or leaked - consider cancelling those runs and restarting them on the latest patch.

#### Workarounds

In case a version upgrade is not possible, avoid passing predictable or guessable values to the `token` parameter of `createWebhook()`. Instead, users can either

* switch from `createWebhook()` to `createHook()` instead and programmatically resume hooks using `resumeHook()` instead of the public webhook endpoint, or
* use `createWebhook()` without passing a user-provided `token`, which uses a non-guessable random `nanoid` by default.

## Which versions are affected by GHSA-9r75-g2cr-3h76?

4 open source packages ship an affected version, including @workflow/core and workflow.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@workflow/core` | npm | All versions | 4.2.0-beta.64 |
| `@workflow/core` | npm | All versions | 4.2.0-beta.64 |
| `workflow` | npm | All versions | 4.2.0-beta.64 |
| `workflow` | npm | All versions | 4.2.0-beta.64 |

## How do I fix GHSA-9r75-g2cr-3h76?

Upgrade @workflow/core to 4.2.0-beta.64 or later.

## Is GHSA-9r75-g2cr-3h76 being exploited?

There is no known exploitation of GHSA-9r75-g2cr-3h76 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-9r75-g2cr-3h76 and fix it if it is affected.

What it is: GHSA-9r75-g2cr-3h76 is an authentication bypass vulnerability in @workflow/core, published on 6 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-9r75-g2cr-3h76 in the wild and no public exploit code.

Affected packages and fixed versions:
- @workflow/core (npm): affected all versions; fixed in 4.2.0-beta.64
- @workflow/core (npm): affected all versions; fixed in 4.2.0-beta.64
- workflow (npm): affected all versions; fixed in 4.2.0-beta.64
- workflow (npm): affected all versions; fixed in 4.2.0-beta.64

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/GHSA-9r75-g2cr-3h76/ (Markdown: https://insights.sbomify.com/GHSA-9r75-g2cr-3h76/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-9r75-g2cr-3h76

---
From sbomify Insights: https://insights.sbomify.com/GHSA-9r75-g2cr-3h76/
Summaries are generated and may contain mistakes; the official description above is the record.