{"id":"CVE-2026-89186","state":"PUBLISHED","title":"mpp writes Payment-Receipt and Cache-Control before the wrapped application runs, letting a consumer's own Cache-Control expose paid responses to shared caches","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.\n\nMPP.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.\n\nThis issue affects mpp: from 0.1.0 before 0.16.2.","publishedAt":"2026-09-16T08:24:15.058Z","updatedAt":"2026-09-16T14:50:44.399Z","severity":{"score":6.3,"label":"Medium","version":"4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N","source":"EEF"},"assigner":"EEF","products":["ZenHive mpp"],"affected":[{"vendor":"ZenHive","product":"mpp","packageName":"mpp","packageURL":"pkg:hex/mpp","defaultStatus":"unaffected","versions":[{"version":"0.1.0","status":"affected","lessThan":"0.16.2","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MPP.Plug'"],"programFiles":["lib/mpp/plug.ex"],"programRoutines":[{"name":"'Elixir.MPP.Plug':call/2"}],"repo":"https://github.com/ZenHive/mpp"},{"vendor":"ZenHive","product":"mpp","packageName":"zenhive/mpp","packageURL":"pkg:github/zenhive/mpp","defaultStatus":"unaffected","versions":[{"version":"2d4d1d94aae7790ae0623063961adbeef171fa71","status":"affected","lessThan":"2fd91a5ecbd0b0ad2a4ac202b79659e8126dbc0b","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MPP.Plug'"],"programFiles":["lib/mpp/plug.ex"],"programRoutines":[{"name":"'Elixir.MPP.Plug':call/2"}],"repo":"https://github.com/ZenHive/mpp"}],"references":["https://github.com/ZenHive/mpp/security/advisories/GHSA-82qh-vrvm-gqvc","https://cna.erlef.org/cves/CVE-2026-89186.html","https://osv.dev/vulnerability/EEF-CVE-2026-89186","https://github.com/ZenHive/mpp/commit/2d4d1d94aae7790ae0623063961adbeef171fa71","https://github.com/ZenHive/mpp/commit/2fd91a5ecbd0b0ad2a4ac202b79659e8126dbc0b"],"weaknesses":["CWE-524"],"ingestedAt":"2026-10-29T20:13:26.108Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/89xxx/CVE-2026-89186.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89186","state":"PUBLISHED","datePublished":"2026-09-16T08:24:15.058Z","dateUpdated":"2026-09-16T14:50:44.399Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-09-11T19:00:02.549Z"},"containers":{"cna":{"title":"mpp writes Payment-Receipt and Cache-Control before the wrapped application runs, letting a consumer's own Cache-Control expose paid responses to shared caches","descriptions":[{"lang":"en","value":"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.\n\nMPP.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.\n\nThis issue affects mpp: from 0.1.0 before 0.16.2."}],"affected":[{"vendor":"ZenHive","product":"mpp","packageName":"mpp","packageURL":"pkg:hex/mpp","defaultStatus":"unaffected","versions":[{"version":"0.1.0","status":"affected","lessThan":"0.16.2","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MPP.Plug'"],"programFiles":["lib/mpp/plug.ex"],"programRoutines":[{"name":"'Elixir.MPP.Plug':call/2"}],"repo":"https://github.com/ZenHive/mpp"},{"vendor":"ZenHive","product":"mpp","packageName":"zenhive/mpp","packageURL":"pkg:github/zenhive/mpp","defaultStatus":"unaffected","versions":[{"version":"2d4d1d94aae7790ae0623063961adbeef171fa71","status":"affected","lessThan":"2fd91a5ecbd0b0ad2a4ac202b79659e8126dbc0b","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MPP.Plug'"],"programFiles":["lib/mpp/plug.ex"],"programRoutines":[{"name":"'Elixir.MPP.Plug':call/2"}],"repo":"https://github.com/ZenHive/mpp"}],"references":[{"url":"https://github.com/ZenHive/mpp/security/advisories/GHSA-82qh-vrvm-gqvc","name":"GitHub Advisory","tags":["related","vendor-advisory"]},{"url":"https://cna.erlef.org/cves/CVE-2026-89186.html","name":"EEF CNA record for CVE-2026-89186","tags":["related"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-89186","name":"OSV record EEF-CVE-2026-89186","tags":["related"]},{"url":"https://github.com/ZenHive/mpp/commit/2d4d1d94aae7790ae0623063961adbeef171fa71","name":"Introducing commit 2d4d1d9 in ZenHive/mpp","tags":["related"]},{"url":"https://github.com/ZenHive/mpp/commit/2fd91a5ecbd0b0ad2a4ac202b79659e8126dbc0b","name":"Fix commit 2fd91a5 in ZenHive/mpp","tags":["patch"]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"NETWORK","baseScore":6.3,"baseSeverity":"MEDIUM","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"LOW","subIntegrityImpact":"NONE","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"LOW","vulnIntegrityImpact":"NONE","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-524","description":"CWE-524 Use of Cache Containing Sensitive Information","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-09-16T08:24:15.058Z"},"configurations":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

Reachable only where the application mounted behind MPP.Plug sets its own Cache-Control on the paid resource, overriding the private the library wrote, and a shared HTTP cache (CDN or reverse proxy) sits in front of that route. An application that sets no Cache-Control of its own keeps the library's private and is not affected.

"},{"base64":false,"type":"text/markdown","value":"Reachable only where the application mounted behind `MPP.Plug` sets its own `Cache-Control` on the paid resource, overriding the `private` the library wrote, and a shared HTTP cache (CDN or reverse proxy) sits in front of that route. An application that sets no `Cache-Control` of its own keeps the library's `private` and is not affected."}],"value":"Reachable only where the application mounted behind MPP.Plug sets its own Cache-Control on the paid resource, overriding the private the library wrote, and a shared HTTP cache (CDN or reverse proxy) sits in front of that route. An application that sets no Cache-Control of its own keeps the library's private and is not affected."}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*","versionEndExcluding":"0.16.2","versionStartIncluding":"0.1.0","vulnerable":true}],"negate":false,"operator":"OR"}],"operator":"AND"}],"credits":[{"lang":"en","type":"finder","value":"E.FU"},{"lang":"en","type":"remediation developer","value":"E.FU"},{"lang":"en","type":"coordinator","value":"Jonatan Männchen / EEF"}],"dateAssigned":"2026-09-15T15:22:44.000Z","impacts":[{"capecId":"CAPEC-204","descriptions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

An unpaid client requesting the same URL through the shared cache receives the cached paid response, including the Payment-Receipt header issued to the paying client. Operators lose the revenue for every cache hit, and the receipt identifying a paid transaction is disclosed to third parties.

"},{"base64":false,"type":"text/markdown","value":"An unpaid client requesting the same URL through the shared cache receives the cached paid response, including the `Payment-Receipt` header issued to the paying client. Operators lose the revenue for every cache hit, and the receipt identifying a paid transaction is disclosed to third parties."}],"value":"An unpaid client requesting the same URL through the shared cache receives the cached paid response, including the Payment-Receipt header issued to the paying client. Operators lose the revenue for every cache hit, and the receipt identifying a paid transaction is disclosed to third parties."}]}],"source":{"discovery":"INTERNAL"},"workarounds":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

In the application mounted behind MPP.Plug, stop setting Cache-Control on paid routes so the library's private survives to the response, or set a directive that is itself safe for a shared cache (private, or no-store). Where the application must set its own caching policy, configure the CDN or reverse proxy not to cache responses carrying a Payment-Receipt header.

"},{"base64":false,"type":"text/markdown","value":"In the application mounted behind `MPP.Plug`, stop setting `Cache-Control` on paid routes so the library's `private` survives to the response, or set a directive that is itself safe for a shared cache (`private`, or `no-store`). Where the application must set its own caching policy, configure the CDN or reverse proxy not to cache responses carrying a `Payment-Receipt` header."}],"value":"In the application mounted behind MPP.Plug, stop setting Cache-Control on paid routes so the library's private survives to the response, or set a directive that is itself safe for a shared cache (private, or no-store). Where the application must set its own caching policy, configure the CDN or reverse proxy not to cache responses carrying a Payment-Receipt header."}]},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-16T14:50:34.541725Z","id":"CVE-2026-89186","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-09-16T14:50:44.399Z"}}]}}}