CVE-2026-113671

ApostropheCMS is an open-source Node.js content management system. From 1.0.0-beta.10 until 1.0.0-beta.13 of the AI helper, an editor with image-generation capability can create a base64-generated image record without a stored provider URL and invoke image acceptance on a deployment using local relative storage with no trusted global base URL. The server resolves the fixed uploads path against a request-controlled Host-derived origin, enabling bounded server-side requests to an attacker-selected host, port, and HTTP origin, but not arbitrary-path retrieval or the stored-provider and absolute-storage configurations. This issue is fixed in AI helper 1.0.0-beta.13.

ApostropheCMS is an open-source Node.js content management system. From 1.0.0-beta.10 until 1.0.0-beta.13 of the AI helper, an editor with image-generation capability can create a base64-generated image record without a stored provider URL and invoke image acceptance on a deployment using local relative storage with no trusted global base URL. The server resolves the fixed uploads path against a request-controlled Host-derived origin, enabling bounded server-side requests to an attacker-selected host, port, and HTTP origin, but not arbitrary-path retrieval or the stored-provider and absolute-storage configurations. This issue is fixed in AI helper 1.0.0-beta.13.

Summary

The @apostrophecms/ai-helper package builds the URL for a server-side image fetch by resolving a storage-relative path against req.baseUrl. When the site does not set a global base URL (the default), req.baseUrl is derived from the incoming HTTP Host header. An authenticated editor can generate a base64 AI image (which is persisted without a stored url) and then send an unauthorized PATCH accept request with an attacker-chosen Host header. The server then issues an outbound GET to the attacker-selected origin, producing a Server-Side Request Forgery primitive that reaches hosts and ports the client cannot otherwise contact. The affected code lives in packages/ai-helper/modules/@apostrophecms/ai-helper-image/index.js.

Root Cause

The image accept route trusts req.baseUrl as a safe origin for constructing an internal fetch target, but req.baseUrl is attacker-influenced whenever the site has no configured base URL. The URL builder concatenates a default local storage path (which is relative, for example /uploads) and resolves it against req.baseUrl; because the left operand is relative, the resulting origin is taken entirely from req.baseUrl. Two protections that exist elsewhere are missing on this path: the generate route enforces an edit capability, but the accept route performs no authorization or ownership check, and no allowlist or validation constrains the resolved origin before the fetch.

packages/ai-helper/modules/@apostrophecms/ai-helper-image/index.js
  aiHelperImageUrl (line 91-92): image.url || new URL(self.uploadfs.getUrl() + `/ai-helper-images/${image._id}.png`, req.baseUrl)
  aiHelperFetchImage (line 64-65): fetch(self.aiHelperImageUrl(req, image))
  apiRoutes.patch['ai-helper/:_id'] (line 314-333): findOne({ _id }) only; no permission or ownership check
packages/apostrophe/modules/@apostrophecms/i18n/index.js
  setPrefixUrls (line 799-820): req.baseUrl falls back to `${req.protocol}://${host}`, host from the Host header when apos.baseUrl is unset

Impact

An attacker who holds a low-privileged editor account (the capability required to generate an AI image, which inserts a base64 record without a stored url and returns its identifier) can coerce the server into issuing outbound GET requests to an origin of their choosing by supplying a crafted Host header on the accept request. This yields SSRF: probing internal hosts and ports that are not reachable from the attacker's network position, and limited semi-blind exfiltration where an image-parseable response at the fixed path becomes a viewable attachment. The request path is fixed to /uploads/ai-helper-images/<id>.png, so only the origin (host, port, and http scheme) is attacker-controlled; arbitrary-path retrieval such as cloud metadata traversal is not reachable through this primitive. No integrity or availability primitive was demonstrated. Exploitation requires the default deployment where no global base URL is configured and local file storage is in use, together with a configured provider that returns base64 image data.

Proof of Concept

Preconditions:
  - ApostropheCMS site with @apostrophecms/ai-helper installed and a configured
    base64-returning image provider.
  - No global base URL configured (apos.baseUrl unset), default local uploadfs.
  - Attacker holds an account with edit capability on at least one content type.

1. Authenticate as the editor and generate a base64 AI image: POST /api/v1/@apostrophecms/image/ai-helper with body {"prompt":"x"}. The response contains the new record identifier <_id>. The persisted record has no url field.
2. Send the accept request with a malicious Host header:

PATCH /api/v1/@apostrophecms/image/ai-helper/<_id> HTTP/1.1
Host: 169.254.169.254
Content-Type: application/json

{"accepted": true}

3. The server derives req.baseUrl as http://169.254.169.254, builds the fetch target…

ApostropheCMS is an open-source Node.js content management system. From 1.0.0-beta.10 until 1.0.0-beta.13 of the AI helper, an editor with image-generation capability can create a base64-generated image record without a stored provider URL and invoke image acceptance on a deployment using local relative storage with no trusted global base URL. The server resolves the fixed uploads path against a request-controlled Host-derived origin, enabling bounded server-side requests to an attacker-selected host, port, and HTTP origin, but not arbitrary-path retrieval or the stored-provider and absolute-storage configurations. This issue is fixed in AI helper 1.0.0-beta.13.

ApostropheCMS is an open-source Node.js content management system. From 1.0.0-beta.10 until 1.0.0-beta.13 of the AI helper, an editor with image-generation capability can create a base64-generated image record without a stored provider URL and invoke image acceptance on a deployment using local relative storage with no trusted global base URL. The server resolves the fixed uploads path against a request-controlled Host-derived origin, enabling bounded server-side requests to an attacker-selected host, port, and HTTP origin, but not arbitrary-path retrieval or the stored-provider and absolute-storage configurations. This issue is fixed in AI helper 1.0.0-beta.13.

Summary

The @apostrophecms/ai-helper package builds the URL for a server-side image fetch by resolving a storage-relative path against req.baseUrl. When the site does not set a global base URL (the default), req.baseUrl is derived from the incoming HTTP Host header. An authenticated editor can generate a base64 AI image (which is persisted without a stored url) and then send an unauthorized PATCH accept request with an attacker-chosen Host header. The server then issues an outbound GET to the attacker-selected origin, producing a Server-Side Request Forgery primitive that reaches hosts and ports the client cannot otherwise contact. The affected code lives in packages/ai-helper/modules/@apostrophecms/ai-helper-image/index.js.

Root Cause

The image accept route trusts req.baseUrl as a safe origin for constructing an internal fetch target, but req.baseUrl is attacker-influenced whenever the site has no configured base URL. The URL builder concatenates a default local storage path (which is relative, for example /uploads) and resolves it against req.baseUrl; because the left operand is relative, the resulting origin is taken entirely from req.baseUrl. Two protections that exist elsewhere are missing on this path: the generate route enforces an edit capability, but the accept route performs no authorization or ownership check, and no allowlist or validation constrains the resolved origin before the fetch.

packages/ai-helper/modules/@apostrophecms/ai-helper-image/index.js
  aiHelperImageUrl (line 91-92): image.url || new URL(self.uploadfs.getUrl() + `/ai-helper-images/${image._id}.png`, req.baseUrl)
  aiHelperFetchImage (line 64-65): fetch(self.aiHelperImageUrl(req, image))
  apiRoutes.patch['ai-helper/:_id'] (line 314-333): findOne({ _id }) only; no permission or ownership check
packages/apostrophe/modules/@apostrophecms/i18n/index.js
  setPrefixUrls (line 799-820): req.baseUrl falls back to `${req.protocol}://${host}`, host from the Host header when apos.baseUrl is unset

Impact

An attacker who holds a low-privileged editor account (the capability required to generate an AI image, which inserts a base64 record without a stored url and returns its identifier) can coerce the server into issuing outbound GET requests to an origin of their choosing by supplying a crafted Host header on the accept request. This yields SSRF: probing internal hosts and ports that are not reachable from the attacker's network position, and limited semi-blind exfiltration where an image-parseable response at the fixed path becomes a viewable attachment. The request path is fixed to /uploads/ai-helper-images/<id>.png, so only the origin (host, port, and http scheme) is attacker-controlled; arbitrary-path retrieval such as cloud metadata traversal is not reachable through this primitive. No integrity or availability primitive was demonstrated. Exploitation requires the default deployment where no global base URL is configured and local file storage is in use, together with a configured provider that returns base64 image data.

Proof of Concept

Preconditions:
  - ApostropheCMS site with @apostrophecms/ai-helper installed and a configured
    base64-returning image provider.
  - No global base URL configured (apos.baseUrl unset), default local uploadfs.
  - Attacker holds an account with edit capability on at least one content type.

1. Authenticate as the editor and generate a base64 AI image: POST /api/v1/@apostrophecms/image/ai-helper with body {"prompt":"x"}. The response contains the new record identifier <_id>. The persisted record has no url field.
2. Send the accept request with a malicious Host header:

PATCH /api/v1/@apostrophecms/image/ai-helper/<_id> HTTP/1.1
Host: 169.254.169.254
Content-Type: application/json

{"accepted": true}

3. The server derives req.baseUrl as http://169.254.169.254, builds the fetch target…