ApostropheCMS: Host header controls server-side image fetch origin in @apostrophecms/ai-helper, enabling authenticated SSRF

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

EPSS

• CVE-2026-113671: 0.33% estimated exploitation activity in the next 30 days; percentile 26.07 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

20 Oct 2026, 18:11 UTC

Last modified by the source

20 Oct 2026, 18:30 UTC

Source last checked

26 Oct 2026, 13:07 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-527g-ff96-x6wj

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-527g-ff96-x6wj

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-527g-ff96-x6wj

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# Patch Next advisory brief: CVE-2026-113671

Advisory: ApostropheCMS: Host header controls server-side image fetch origin in @apostrophecms/ai-helper, enabling authenticated SSRF
IDs: CVE-2026-113671, GHSA-527g-ff96-x6wj
Record: https://patchnext.com/advisories/cve-2026-113671 (revision 3, source checked 26 Oct 2026, 13:07 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @apostrophecms/ai-helper 1.0.0-beta.13. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @apostrophecms/ai-helper: affected >= 1.0.0-beta.10, < 1.0.0-beta.13; fixed in 1.0.0-beta.13

## Suggested inspection (read-only)
- `npm ls @apostrophecms/ai-helper --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @apostrophecms/ai-helper.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-527g-ff96-x6wj (GitHub-reviewed advisory GHSA-527g-ff96-x6wj lists affected ranges: npm @apostrophecms/ai-helper >=1.0.0-beta.10 <1.0.0-beta.13)
- Verified: https://osv.dev/vulnerability/GHSA-527g-ff96-x6wj (OSV record GHSA-527g-ff96-x6wj lists affected ranges: npm @apostrophecms/ai-helper >=1.0.0-beta.10 <1.0.0-beta.13 (fixed))

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