CVE-2026-89186 Information disclosure in mpp
Attackers can access paid content via shared caches because the library's cache-control headers are overridden by the application, exposing sensitive data to unpaid users.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89186?
CVE-2026-89186 is a medium-severity vulnerability in ZenHive mpp, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Use of Cache Containing Sensitive Information in ZenHive mpp allows a shared HTTP cache to store a paid response and serve it to clients that never paid.
MPP.Plug.verify_credential in lib/mpp/plug.ex sets payment-receipt and cache-control: private on the connection before the wrapped application runs, and registers no register_before_send/2 callback. Plug.Conn.put_resp_header/3 replaces an existing header, so a mounting application that sets its own cache-control on the paid resource (for example public, max-age=3600) silently overrides the private the library relies on, and a CDN or reverse proxy can then store the paid 200 together with its Payment-Receipt and serve both to unpaid clients. The library-level guarantee is therefore defeatable by the application it protects. For the same reason a downstream non-2xx response still carried Payment-Receipt, issuing a receipt for a response that delivered no resource.
This issue affects mpp: from 0.1.0 before 0.16.2.
Weakness: CWE-524
Which versions are affected by CVE-2026-89186?
1 open source package ship an affected version, including mpp.
| Package | Affected | Fixed in |
|---|---|---|
mpp Hex | From 0.1.0 | 0.16.2 |
How do I fix CVE-2026-89186?
Upgrade mpp to 0.16.2 or later.
Is CVE-2026-89186 being exploited?
There is no known exploitation of CVE-2026-89186 in the wild and no public exploit code.
Sources
Also known as EEF-CVE-2026-89186, GHSA-4h6w-pvrh-g28p, GHSA-82qh-vrvm-gqvc.