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

{
  "id": "65c73377d9c1af95623a0af5d9f6f80ffab5f96823f6ae7b7ff822cf1bbb98f6",
  "url": "https://osv.dev/vulnerability/GHSA-527g-ff96-x6wj",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ApostropheCMS: Host header controls server-side image fetch origin in @apostrophecms/ai-helper, enabling authenticated SSRF",
    "summary": "## 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. ```text packages/ai-helper/modules/@apostro",
    "evidence": "osv:GHSA-527g-ff96-x6wj",
    "products": [
      {
        "name": {
          "value": "@apostrophecms/ai-helper",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "1.0.0-beta.13",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "medium",
    "structured": {
      "id": "GHSA-527g-ff96-x6wj",
      "aliases": [
        "CVE-2026-113671",
        "GHSA-527g-ff96-x6wj"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "1.0.0-beta.10"
                },
                {
                  "fixed": "1.0.0-beta.13"
                }
              ]
            }
          ],
          "package": {
            "name": "@apostrophecms/ai-helper",
            "purl": "pkg:npm/%40apostrophecms/ai-helper",
            "ecosystem": "npm"
          },
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-527g-ff96-x6wj/GHSA-527g-ff96-x6wj.json"
          }
        }
      ],
      "modified": "2026-10-20T18:30:03.589840564Z",
      "provider": "osv",
      "references": [
        "https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-527g-ff96-x6wj",
        "https://github.com/apostrophecms/apostrophe/commit/9500b8b0e1d630d5e07fbb5fd2c25ed0943845ce",
        "https://github.com/apostrophecms/apostrophe/commit/f84fd41cbf6c22eb8d0008fc9c25df1f7130b350",
        "https://github.com/apostrophecms/apostrophe",
        "https://github.com/apostrophecms/apostrophe/releases/tag/@apostrophecms/ai-helper@1.0.0-beta.13"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-918"
        ],
        "severity": "MODERATE",
        "github_reviewed": true,
        "nvd_published_at": null,
        "github_reviewed_at": "2026-10-20T18:11:01Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-113671",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 390145,
  "published_at": "2026-10-20T18:11:01+00:00"
}