{"id":"GHSA-q2pj-8v84-9mh5","summary":"Arcane Backend: Unauthenticated reflected XSS via SVG color parameter enables admin account takeover","details":"## Summary\n\nThe unauthenticated `GET /api/app-images/logo` endpoint reflects a user-supplied `color` query parameter into the body of an SVG document via `strings.ReplaceAll` with no escaping. The substitution lands inside a `\u003cstyle\u003e` element of the embedded `logo.svg`, allowing an attacker to close the style block and inject executable `\u003cscript\u003e` content. Because the response is served as `image/svg+xml` and Arcane sets no Content-Security-Policy or `X-Content-Type-Options` headers, navigating a logged-in admin victim to a crafted URL executes attacker-controlled JavaScript in Arcane's origin and rides the victim's HttpOnly JWT cookie to fully compromise the admin account.\n\n## Details\n\nThe route is registered in `backend/internal/huma/handlers/appimages.go:53-61` with an explicitly empty security requirement, marking it as public:\n\n```go\nhuma.Register(api, huma.Operation{\n    OperationID: \"get-logo\",\n    Method:      http.MethodGet,\n    Path:        \"/app-images/logo\",\n    ...\n    Security:    []map[string][]string{}, // explicit: no auth\n}, h.GetLogo)\n```\n\n`backend/internal/huma/middleware/auth.go:209-213` honors the empty `Security` value by returning `reqs.isRequired == false` and short-circuiting with `next(ctx)`, so no JWT/API-key check runs.\n\n`GetLogoInput.Color` (`appimages.go:23`) is declared with no validation tags:\n\n```go\ntype GetLogoInput struct {\n    Full  bool   `query:\"full\" default:\"false\" ...`\n    Color string `query:\"color\" doc:\"Optional accent color override ...\"`\n}\n```\n\nThe handler passes the value straight through `getImageWithColor` → `ApplicationImagesService.GetImageWithColor` → `applyAccentColorToSVG` (`backend/internal/services/app_images_service.go:79-105`):\n\n```go\nsvgStr = strings.ReplaceAll(svgStr, \"fill:#6D28D9\", fmt.Sprintf(\"fill:%s\", accentColor))\nsvgStr = strings.ReplaceAll(svgStr, \"fill:#6d28d9\", fmt.Sprintf(\"fill:%s\", accentColor))\n```\n\nThe bundled `backend/resources/images/logo.svg` contains:\n\n```xml\n\u003cstyle id=\"style1\" type=\"text/css\"\u003e.st0{fill:#6d28d9}\u003c/style\u003e\n```\n\nso a `color` value like `red}\u003c/style\u003e\u003cscript\u003efetch('/api/users',...)\u003c/script\u003e\u003cstyle\u003ex{` produces a valid SVG that closes the `\u003cstyle\u003e` element and embeds a `\u003cscript\u003e` element. The response Content-Type is `image/svg+xml` (from `pkg/utils/image/image_util.go`), and a grep of the backend confirms no `Content-Security-Policy`, `X-Content-Type-Options`, or framing headers are emitted on any route.\n\nBrowsers execute scripts in SVG documents loaded as top-level navigations or via `\u003ciframe src=…\u003e` / `window.open(…)`. The execution context is `origin(arcane-host)`, so the victim's `__Host-token` / `token` HttpOnly JWT cookie (recognized by `extractTokenFromCookieHeaderInternal` at `auth.go:274-286`) is automatically attached to subsequent same-origin `fetch()` calls. From there the attacker can invoke any privileged API the victim possesses — most damagingly `POST /api/users` to create a new admin account, after which the attacker has standalone admin access to manage Docker containers, registries, GitOps secrets, and SSH/registry credentials stored by Arcane.\n\n## Impact\n\n- Same-origin script execution from an unauthenticated, reachable URL — only user interaction (clicking/visiting the crafted link) is required.\n- Full session-riding against any authenticated user, including admins. Because Arcane manages Docker daemons, container exec, image registries, and GitOps repositories, an attacker who lands script execution as an admin victim can:\n  - Create persistent attacker-controlled admin accounts via `POST /api/users`.\n  - Read/modify secrets stored in environments, registries, and Git repositories the admin can access.\n  - Start or exec into containers on connected Docker hosts.\n- HttpOnly cookies do not mitigate the issue — cookies are auto-attached to same-origin `fetch()`. Absence of CSP and `X-Content-Type-Options: nosniff` removes available defenses-in-depth.\n\nDefense-in-depth — add to all responses (and especially to `/api/app-images/*`):\n\n- `X-Content-Type-Options: nosniff`\n- `Content-Security-Policy: default-src 'none'; style-src 'unsafe-inline'; img-src 'self' data:` on the SVG image responses (or the most permissive policy compatible with the frontend on app routes).\n- Consider serving these images with `Content-Disposition: inline` and from a separate cookie-less origin to remove the same-origin session-riding primitive entirely.\n\nAlso enforce the same allowlist on the settings write path (`SettingsService` → `AccentColor`) so a stored XSS variant cannot be introduced via the settings API.","aliases":["CVE-2026-45627","GO-2026-5561"],"modified":"2026-06-25T23:11:29.838847344Z","published":"2026-05-18T14:19:26Z","database_specific":{"github_reviewed_at":"2026-05-18T14:19:26Z","nvd_published_at":"2026-05-29T18:17:10Z","cwe_ids":["CWE-79"],"severity":"HIGH","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/getarcaneapp/arcane/security/advisories/GHSA-q2pj-8v84-9mh5"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-45627"},{"type":"PACKAGE","url":"https://github.com/getarcaneapp/arcane"}],"affected":[{"package":{"name":"github.com/getarcaneapp/arcane/backend","ecosystem":"Go","purl":"pkg:golang/github.com/getarcaneapp/arcane/backend"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.19.0"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 1.18.1","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-q2pj-8v84-9mh5/GHSA-q2pj-8v84-9mh5.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N"}]}