Description

Payload Plugins is a collection of plugins designed to enhance Payload CMS. In 0.7.0, @jhb.software/payload-alt-text-plugin exposes POST /api/alt-text-plugin/generate and POST /api/alt-text-plugin/bulk with a default guard that accepts any authenticated user, while alt-text/src/endpoints/generateAltText.ts and alt-text/src/endpoints/bulkGenerateAltTexts.ts call req.payload.findByID and req.payload.update without overrideAccess: false. Payload therefore defaults overrideAccess to true and skips the target collection's read and update access functions. An authenticated low-privilege user can supply id, collection, locale, and update values to read arbitrary protected upload documents and overwrite their alt and keywords fields, even when the collection permits those operations only to administrators. A control Local API call with overrideAccess: false is denied, confirming that the plugin endpoint bypasses otherwise effective collection rules. This vulnerability is fixed in 0.8.0.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.1",
  "pubDate": "2026-09-15T16:17:17.110Z",
  "pubdate": "2026-09-15T16:17:17.110Z",
  "executiveSummary": "The @jhb.software/payload-alt-text-plugin, a component for Payload CMS, is susceptible to an authorization bypass vulnerability.\nThis security flaw stems from the insecure implementation of backend API endpoints that handle document modification without respecting established access control policies.\nAffected versions include 0.7.0. The vulnerability allows an authenticated low-privilege user to bypass restrictive read and update access controls defined on specific collections within Payload CMS.\nBy interacting with the POST /api/alt-text-plugin/generate and POST /api/alt-text-plugin/bulk endpoints, an attacker can read sensitive metadata from protected upload documents and perform unauthorized modifications to 'alt' and 'keywords' fields.\nThe risk is significant as it facilitates unauthorized data manipulation and potential exposure of sensitive information that should be limited to administrative users.\nSuccessful exploitation requires the attacker to have at least a low-privileged authenticated session within the application. The vulnerability underscores the danger of improper API configuration in CMS plugins where default settings may inadvertently elevate privileges during Local API operations.",
  "technicalDetails": "The vulnerability resides in the interaction between the plugin's custom endpoints and the Payload CMS Local API. Specifically, the files alt-text/src/endpoints/generateAltText.ts and alt-text/src/endpoints/bulkGenerateAltTexts.ts initiate calls to req.payload.findByID and req.payload.update.\nIn Payload CMS, the Local API functions default the overrideAccess property to true when it is not explicitly set to false. By failing to explicitly set overrideAccess: false, the plugin instructs the underlying Payload engine to bypass the configured access control functions defined on the target collections.\nThe attack flow commences with the attacker authenticated as a low-privileged user. They craft HTTP POST requests to the endpoints /api/alt-text-plugin/generate or /api/alt-text-plugin/bulk. These requests include user-supplied parameters such as 'id', 'collection', 'locale', and specific 'update' values.\nUpon receiving the request, the plugin executes the Local API calls. Because of the missing access override protection, the engine processes these requests with administrative-level privileges, ignoring the restriction rules typically governed by the collection schema.\nThis allows the attacker to read arbitrary document data and overwrite fields—specifically 'alt' and 'keywords'—that should be strictly protected. The validity of this bypass is confirmed by comparing the plugin's execution against a direct Local API call configured with overrideAccess: false, which is correctly denied by the system security policy.\nThis flaw highlights a critical failure in the plugin's authorization logic, where a default guard merely verifies the presence of an authenticated session rather than validating the user's granular permissions against the specific record or collection being accessed. Post-exploitation impact allows for the corruption of document metadata and potential indirect information disclosure, impacting the integrity of the media library management within the CMS instance."
}