{"id":"CVE-2026-21885","aliases":["GHSA-xwh2-742g-w3wp","GO-2026-4287"],"url":"https://o3.security/vulnerability/CVE-2026-21885","summary":"Miniflux Media Proxy SSRF via /proxy endpoint allows access to internal network resources","details":"### Summary\nMiniflux's media proxy endpoint (`GET /proxy/{encodedDigest}/{encodedURL}`) can be abused to perform Server-Side Request Forgery (SSRF). An authenticated user can cause Miniflux to generate a signed proxy URL for attacker-chosen media URLs embedded in feed entry content, including internal addresses (e.g., localhost, private RFC1918 ranges, or link-local metadata endpoints). Requesting the resulting `/proxy/...` URL makes Miniflux fetch and return the internal response.\n\n### Details\n- **Vulnerable route**: `GET /proxy/{encodedDigest}/{encodedURL}` (accessible without authentication, but requires a server-generated HMAC-signed URL)\n- **Handler**: `internal/ui/proxy.go` (`(*handler).mediaProxy`)\n- **Trigger**: entry content is rewritten to proxy media URLs (e.g., `mediaproxy.RewriteDocumentWithAbsoluteProxyURL(...)`), producing signed `/proxy/...` URLs.\n- **Root cause**: the proxy validates the URL scheme and HMAC signature, but does not restrict target hosts/IPs. As a result, requests to loopback/private/link-local addresses are allowed and fetched by the server.\n\n### PoC\n1) Run Miniflux 2.2.15 with default configuration (media proxy enabled by default: `MEDIA_PROXY_MODE=http-only`).\n\n2) Log in with any normal user account.\n\n3) Subscribe to a feed you control that contains an entry with an image URL pointing to an internal address reachable from the Miniflux server, e.g.:\n   - `<img src=\"http://<internal-target>/secret\">`\n   (Note: `<internal-target>` must be reachable *from the Miniflux process/network*; in containerized setups, `127.0.0.1` may not refer to the host.)\n\n4) Open the entry and locate the rewritten media proxy URL (`/proxy/<encodedDigest>/<encodedURL>`) in the rendered HTML/page source.\n\n5) Request the `/proxy/...` URL.\nExpected (vulnerable): Miniflux fetches the internal URL and returns the internal response (SSRF).\n\n### Impact\n**Type**: SSRF (Server-Side Request Forgery) via media proxy  \n**Who is impacted**: Miniflux instances with media proxy enabled (default configuration typically enables it for HTTP/mixed content handling).  \n**Impact**: attackers with a valid Miniflux account can fetch internal resources reachable from the Miniflux server (e.g., localhost services, private network services, and link-local endpoints such as 169.254.169.254), potentially exposing sensitive data.\n\n### Suggested CVSS (v3.1)\n`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N` (Base 6.5)\n\n\n\n\nIf there any questions or issues reproducing this, please contact: jeongwoolee340@gmail.com","published":"2026-01-08T13:57:25.445Z","modified":"2026-10-28T02:30:43.565662587Z","cvss":{"score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"miniflux.app/v2","fixedVersion":"2.2.16"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/21xxx/CVE-2026-21885.json"},{"type":"ADVISORY","url":"https://github.com/miniflux/v2/security/advisories/GHSA-xwh2-742g-w3wp"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-21885"},{"type":"PACKAGE","url":"https://github.com/miniflux/v2"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:43.565662587Z"}}