Glean: Server-Side Request Forgery (SSRF) with Full Response Disclosure via Malicious RSS Feed in /api/feeds/discover

Glean is a self-hosted RSS reader and personal knowledge management tool. Prior to 0.2.6, POST /api/feeds/discover passes an attacker-supplied feed_url to discover_feed(feed_url), creates a subscription through FeedService.create_subscription(), and enqueues fetch_feed_task. The background path calls fetch_feed(feed.url) and parse_feed(), which assigns each RSS item link to ParsedEntry.url. The task then passes ParsedEntry.url to fetch_and_extract_fulltext(parsed_entry.url) without network-level validation in backend/packages/rss/glean_rss/extractor.py and backend/apps/worker/glean_worker/tasks/feed_fetcher.py. A malicious feed can therefore make the server request private, loopback, link-local, or cloud-metadata resources. The fetched response is stored in Entry.content and can be retrieved through GET /api/entries/{id}, producing non-blind server-side request forgery with full response disclosure. This can bypass network perimeters, probe internal services and ports, expose internal configuration or web content, and potentially disclose cloud metadata access tokens. This issue is fixed in version 0.2.6.