Summary
Miniflux'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.
Details
- Vulnerable route:
GET /proxy/{encodedDigest}/{encodedURL}(accessible without authentication, but requires a server-generated HMAC-signed URL) - Handler:
internal/ui/proxy.go((*handler).mediaProxy) - Trigger: entry content is rewritten to proxy media URLs (e.g.,
mediaproxy.RewriteDocumentWithAbsoluteProxyURL(...)), producing signed/proxy/...URLs. - 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.
PoC
Run Miniflux 2.2.15 with default configuration (media proxy enabled by default:
MEDIA_PROXY_MODE=http-only).Log in with any normal user account.
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.:
<img src="http://<internal-target>/secret">
(Note:<internal-target>must be reachable from the Miniflux process/network; in containerized setups,127.0.0.1may not refer to the host.)
Open the entry and locate the rewritten media proxy URL (
/proxy/<encodedDigest>/<encodedURL>) in the rendered HTML/page source.Request the
/proxy/...URL.
Expected (vulnerable): Miniflux fetches the internal URL and returns the internal response (SSRF).
Suggested CVSS (v3.1)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N (Base 6.5)
If there any questions or issues reproducing this, please contact: [email protected]
Impact
Type: SSRF (Server-Side Request Forgery) via media proxy
Who is impacted: Miniflux instances with media proxy enabled (default configuration typically enables it for HTTP/mixed content handling).
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.
Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.
CVE-2026-21885 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.2.16); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-21885? CVE-2026-21885 is a medium-severity server-side request forgery (SSRF) vulnerability in miniflux.app/v2 (go), affecting versions <= 2.2.15. It is fixed in 2.2.16. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
- How severe is CVE-2026-21885? CVE-2026-21885 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of miniflux.app/v2 are affected by CVE-2026-21885? miniflux.app/v2 (go) versions <= 2.2.15 is affected.
- Is there a fix for CVE-2026-21885? Yes. CVE-2026-21885 is fixed in 2.2.16. Upgrade to this version or later.
- Is CVE-2026-21885 exploitable, and should I be worried? Whether CVE-2026-21885 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-21885 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-21885? Upgrade
miniflux.app/v2to 2.2.16 or later.