CVE-2026-89186

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.

• https://github.com/ZenHive/mpp/commit/2d4d1d94aae7790ae0623063961adbeef171fa71
• https://github.com/ZenHive/mpp/commit/2fd91a5ecbd0b0ad2a4ac202b79659e8126dbc0b
• https://github.com/ZenHive/mpp/security/advisories/GHSA-82qh-vrvm-gqvc

• https://cna.erlef.org/cves/CVE-2026-89186.html
• https://github.com/ZenHive/mpp/commit/2d4d1d94aae7790ae0623063961adbeef171fa71
• https://github.com/ZenHive/mpp/commit/2fd91a5ecbd0b0ad2a4ac202b79659e8126dbc0b
• https://github.com/ZenHive/mpp/security/advisories/GHSA-82qh-vrvm-gqvc
• https://osv.dev/vulnerability/EEF-CVE-2026-89186

• HIGHCVE-2026-25703PoC

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