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

Not scored Published 6 Mar 2026

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

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

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	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.

Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.

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.