{"id":"EEF-CVE-2026-82750","summary":"Unbounded EIP-7702 authorization list in mpp Tempo fee-payer sponsorship inflates gas cost and sponsors account delegation","details":"## Summary\n\nImproper Validation of Specified Quantity in Input in ZenHive mpp allows an unauthenticated remote client to inflate the fee-payer's gas cost per sponsored payment by a large multiplier and to have the sponsor pay for EIP-7702 account delegations of the client's choosing.\n\nWhen the server sponsors Tempo payments, `MPP.Methods.Tempo.FeePayerPolicy.measure/3` in `lib/mpp/methods/tempo/fee_payer_policy.ex` bounds the gas fields, the fee budget, the validity window and the access list of the client-signed `0x76` envelope, but never reads its `aa_authorization_list` field. Every signed delegation in that list is charged as intrinsic gas before the payment call runs, so a client attaching delegations from throwaway authority keys makes the sponsor pay for them within the default `gas_limit` ceiling. At the reporter's default of seven entries the sponsored cost rises from about 46,575 gas to about 1,884,087 gas. Because each entry is applied as a persistent set-code delegation, a client can also upgrade its own accounts to delegated code at the sponsor's expense.\n\nThis issue affects mpp: from 0.2.0 before 0.16.1.\n\n## Workarounds\n\nDisable Tempo fee sponsorship by leaving `\"fee_payer\"` at its default of `false` and setting no `fee_payer_url`, so the client pays its own gas. Where sponsorship must stay enabled, lower the `max_gas` override in `fee_payer_policy` to just above what a legitimate sponsored payment needs (a TIP-20 transfer is roughly 50,000 gas), so an envelope padded with delegations either fails the policy or runs out of gas at a bounded cost. This bounds the inflation without closing it.\n\n## Configurations\n\nOnly deployments that enable Tempo server-side fee sponsorship are affected, through `\"fee_payer\" =\u003e true` in `method_config` with either local co-signing (`fee_payer_private_key`) or hosted sponsorship (`fee_payer_url`). Sponsorship is disabled by default.","aliases":["CVE-2026-82750","GHSA-5qrp-r24c-w6jr"],"modified":"2026-09-08T16:30:05.263051328Z","published":"2026-09-06T16:08:41.089Z","database_specific":{"capec_ids":["CAPEC-130"],"cpe_ids":["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-1284"]},"references":[{"type":"ADVISORY","url":"https://github.com/ZenHive/mpp/security/advisories/GHSA-5qrp-r24c-w6jr"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-82750.html"},{"type":"FIX","url":"https://github.com/ZenHive/mpp/commit/0482572b47e1ffe1537ab80ab613d47b92833c2d"},{"type":"PACKAGE","url":"https://hex.pm/packages/mpp"}],"affected":[{"package":{"name":"mpp","ecosystem":"Hex","purl":"pkg:hex/mpp"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.2.0"},{"fixed":"0.16.1"}]}],"versions":["0.10.0","0.11.0","0.12.0","0.13.0","0.14.0","0.15.0","0.16.0","0.2.0","0.3.0","0.3.1","0.3.2","0.4.0","0.6.0","0.6.1","0.6.2","0.6.3","0.6.4","0.7.0","0.8.0","0.9.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-82750.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/ZenHive/mpp","events":[{"introduced":"d29d54e507918db00a5b65d90136b73166c017d7"},{"fixed":"0482572b47e1ffe1537ab80ab613d47b92833c2d"}]}],"versions":["v0.16.0","v0.15.0","v0.14.0","v0.13.0","v0.12.0","v0.11.0","v0.10.0","v0.9.0","v0.8.0","v0.7.0","v0.6.4","v0.6.3","v0.6.1","v0.6.0","v0.5.1","v0.4.0","v0.3.0","v0.2.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-82750.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N"}],"credits":[{"name":"Kian Kai Ang","type":"FINDER"},{"name":"Kian Kai Ang","type":"REPORTER"},{"name":"E.FU","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"COORDINATOR"}]}