{"id":"CVE-2026-82750","aliases":["GHSA-5qrp-r24c-w6jr"],"url":"https://o3.security/vulnerability/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## Workaround\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## Configuration\n\nOnly deployments that enable Tempo server-side fee sponsorship are affected, through \"fee\\_payer\" => true in method\\_config with either local co-signing (fee\\_payer\\_private\\_key) or hosted sponsorship (fee\\_payer\\_url). Sponsorship is disabled by default.","published":"2026-09-06T16:08:41.089Z","modified":"2026-09-06T16:25:37.575213674Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Hex","name":"mpp","fixedVersion":"0.16.1"}],"fix":{"url":"https://github.com/ZenHive/mpp/commit/0482572b47e1ffe1537ab80ab613d47b92833c2d","label":"ZenHive/mpp@0482572"},"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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-06T16:25:37.575213674Z"}}