{"id":"CVE-2026-59694","aliases":["EEF-CVE-2026-59694","EUVD-2026-45159","GHSA-qpxh-ff8m-c62v","GHSA-r4hx-mhrp-xf73"],"status":"published","title":"Unbounded access list in mpp Tempo fee-payer inflates gas cost per payment","description":"Improper Validation of Specified Quantity in Input in ZenHive mpp allows an unauthenticated remote client to inflate the fee-payer's gas cost per payment by a large multiplier, degrading the sponsor's operating margin.\n\nWhen the mpp Elixir library is configured as fee payer (fee_payer: true), MPP.Tempo.Transaction.cosign_fee_payer/3 re-signs the client-supplied base fields of the 0x76 AASigned envelope verbatim, including the EIP-2930 access list, without validating its length or contents. EIP-2930 access list entries incur intrinsic gas (~2,400 gas per address, plus 1,900 gas per storage key) charged before any opcode executes, regardless of whether the listed addresses are ever touched. A malicious client submits a valid transferWithMemo call alongside a large number of fabricated access-list entries. The server co-signs and broadcasts the transaction. The intended transfer executes normally, but the fee-payer wallet pays a large multiple of the expected gas cost with no corresponding on-chain work.\n\nAt the maintainer's default of 137 access-list entries (fitting within Bandit's 10,000-byte per-header-field limit) and 100 Gwei max_fee_per_gas, per-payment gas cost rises from ~51,287 to ~380,087 gas, a 7.4x multiplier. Sustained abuse destroys the sponsor's operating margin on low-cost payments and, over time, drains the fee-payer wallet.\n\nThis issue affects mpp: from 0.2.0 before 0.6.0.","severity":{"version":"4.0","score":8.3,"vector":"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","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00382,"percentile":0.32722,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-1284","CWE-20"],"published":"2026-07-17T10:11:49Z","modified":"2026-10-28T02:30:22Z","fixes":[{"ecosystem":"Hex","package":"mpp","fixed_in":["0.6.0"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"Hex","package":"mpp","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.2.0"},{"fixed":"0.6.0"}]}]},{"source":"osv","ecosystem":"Hex","package":"mpp","ranges":[{"type":"SEMVER","events":[{"introduced":"0.2.0"},{"fixed":"0.6.0"}]}],"versions":["0.2.0","0.3.0","0.3.1","0.3.2","0.4.0"]},{"source":"osv","ecosystem":"Hex","package":"mpp","ranges":[{"type":"SEMVER","events":[{"introduced":"0.2.0"},{"fixed":"0.6.0"}]}],"versions":["0.2.0","0.3.0","0.3.1","0.3.2","0.4.0"]}],"products":[{"vendor":"zenhive","product":"mpp"}],"references":[{"url":"https://github.com/ZenHive/mpp/security/advisories/GHSA-qpxh-ff8m-c62v","tags":["vendor-advisory","related","exploit","advisory","web"]},{"url":"https://cna.erlef.org/cves/CVE-2026-59694.html","tags":["related","web"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-59694","tags":["related","web"]},{"url":"https://github.com/ZenHive/mpp/commit/5d6338e2334084c5f2a78cfcca474830733ed7e8","tags":["patch","fix","web"]},{"url":"https://github.com/ZenHive/mpp/releases/tag/v0.6.0","tags":["web"]},{"url":"https://github.com/advisories/GHSA-qpxh-ff8m-c62v"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-59694","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-r4hx-mhrp-xf73"},{"url":"https://github.com","tags":["web"]},{"url":"https://repo.hex.pm","tags":["web"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59694.json","tags":["advisory"]},{"url":"https://github.com/ZenHive/mpp","tags":["package"]},{"url":"https://hex.pm/packages/mpp","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-59694","title":"Unbounded access list in mpp Tempo fee-payer inflates gas cost per payment","description":"Improper Validation of Specified Quantity in Input in ZenHive mpp allows an unauthenticated remote client to inflate the fee-payer's gas cost per payment by a large multiplier, degrading the sponsor's operating margin.\n\nWhen the mpp Elixir library is configured as fee payer (fee_payer: true), MPP.Tempo.Transaction.cosign_fee_payer/3 re-signs the client-supplied base fields of the 0x76 AASigned envelope verbatim, including the EIP-2930 access list, without validating its length or contents. EIP-2930 access list entries incur intrinsic gas (~2,400 gas per address, plus 1,900 gas per storage key) charged before any opcode executes, regardless of whether the listed addresses are ever touched. A malicious client submits a valid transferWithMemo call alongside a large number of fabricated access-list entries. The server co-signs and broadcasts the transaction. The intended transfer executes normally, but the fee-payer wallet pays a large multiple of the expected gas cost with no corresponding on-chain work.\n\nAt the maintainer's default of 137 access-list entries (fitting within Bandit's 10,000-byte per-header-field limit) and 100 Gwei max_fee_per_gas, per-payment gas cost rises from ~51,287 to ~380,087 gas, a 7.4x multiplier. Sustained abuse destroys the sponsor's operating margin on low-cost payments and, over time, drains the fee-payer wallet.\n\nThis issue affects mpp: from 0.2.0 before 0.6.0.","status":"published","published":"2026-07-17T10:11:49.192Z","modified":"2026-07-18T04:12:36.335Z","cvss":[{"version":"4.0","score":8.3,"vector":"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","level":"high","assessor":"cna"}],"cwes":["CWE-1284"],"updated_at":"2026-11-02T14:19:58.560602Z"}],"euvd":[{"id":"EUVD-2026-45159","description":"Improper Validation of Specified Quantity in Input in ZenHive mpp allows an unauthenticated remote client to inflate the fee-payer's gas cost per payment by a large multiplier, degrading the sponsor's operating margin.\n\nWhen the mpp Elixir library is configured as fee payer (fee_payer: true), MPP.Tempo.Transaction.cosign_fee_payer/3 re-signs the client-supplied base fields of the 0x76 AASigned envelope verbatim, including the EIP-2930 access list, without validating its length or contents. EIP-2930 access list entries incur intrinsic gas (~2,400 gas per address, plus 1,900 gas per storage key) charged before any opcode executes, regardless of whether the listed addresses are ever touched. A malicious client submits a valid transferWithMemo call alongside a large number of fabricated access-list entries. The server co-signs and broadcasts the transaction. The intended transfer executes normally, but the fee-payer wallet pays a large multiple of the expected gas cost with no corresponding on-chain work.\n\nAt the maintainer's default of 137 access-list entries (fitting within Bandit's 10,000-byte per-header-field limit) and 100 Gwei max_fee_per_gas, per-payment gas cost rises from ~51,287 to ~380,087 gas, a 7.4x multiplier. Sustained abuse destroys the sponsor's operating margin on low-cost payments and, over time, drains the fee-payer wallet.\n\nThis issue affects mpp: from 0.2.0 before 0.6.0.","status":"published","published":"2026-07-17T10:11:49Z","modified":"2026-07-18T04:12:36Z","cvss":[{"version":"4.0","score":8.3,"vector":"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","level":"high"}],"updated_at":"2026-11-02T18:19:50.065723Z"}],"ghsa":[{"id":"GHSA-qpxh-ff8m-c62v","title":"mpp vulnerable to Gas Draining with access list","description":"### Details\nWhen the server acts as the fee_payer, `mpp` Elixir 0.4.0 copies the client-supplied EIP-2930 access list verbatim into the cosigned fee-payer transaction. In `cosign_fee_payer`, the server re-signs the raw `base_fields` (index 5 of the 0x76 AASigned envelope) without inspecting the access list field, which is part of the signed payload.\n\nAccess list gas is charged **intrinsically** — before any opcode executes — regardless of whether the listed addresses are ever touched.\n\nAn attacker submits a valid `transferWithMemo` alongside fabricated address-only access list entries. The server validates calldata and amount but never inspects `access_list` length. It cosigns and broadcasts a transaction that costs the fee-payer wallet `N × 2,400` extra gas per request with no corresponding work performed on-chain.\n\nAt the default of 137 entries and 100 Gwei `max_fee_per_gas`, this inflates the fee-payer cost from the normal ~51,287 gas to ~380,087 gas — a **7.4× multiplier** — while staying within Bandit's default 10,000-byte per-header-field limit (verified empirically).\n\n### PoC\nThe PoC is provided below. It is configured to reproduce the attack on Tempo Moderate testnet within a Docker environment. Download the PoC and run:\n```bash\nunzip mpp_elixir_PoC.zip\ncd mpp_elixir\ndocker build -t mpp-elixir-access-list .\ndocker run --rm mpp-elixir-access-list\n``` \nThere are more details in `mpp_elixir/README.md`\n\n### Impact\nA malicious client can force the server to pay ~**7.4x** the normal transaction fee. This dramatically increases operational costs and completely destroys the profit margin on low-cost items.","status":"published","published":"2026-09-25T21:45:16Z","modified":"2026-09-25T21:45:26Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N","level":"medium"}],"cwes":["CWE-20"],"updated_at":"2026-11-02T14:41:22.654187Z"},{"id":"GHSA-r4hx-mhrp-xf73","title":"Improper Validation of Specified Quantity in Input in ZenHive mpp allows an unauthenticated...","description":"Improper Validation of Specified Quantity in Input in ZenHive mpp allows an unauthenticated remote client to inflate the fee-payer's gas cost per payment by a large multiplier, degrading the sponsor's operating margin.\n\nWhen the mpp Elixir library is configured as fee payer (fee_payer: true), MPP.Tempo.Transaction.cosign_fee_payer/3 re-signs the client-supplied base fields of the 0x76 AASigned envelope verbatim, including the EIP-2930 access list, without validating its length or contents. EIP-2930 access list entries incur intrinsic gas (~2,400 gas per address, plus 1,900 gas per storage key) charged before any opcode executes, regardless of whether the listed addresses are ever touched. A malicious client submits a valid transferWithMemo call alongside a large number of fabricated access-list entries. The server co-signs and broadcasts the transaction. The intended transfer executes normally, but the fee-payer wallet pays a large multiple of the expected gas cost with no corresponding on-chain work.\n\nAt the maintainer's default of 137 access-list entries (fitting within Bandit's 10,000-byte per-header-field limit) and 100 Gwei max_fee_per_gas, per-payment gas cost rises from ~51,287 to ~380,087 gas, a 7.4x multiplier. Sustained abuse destroys the sponsor's operating margin on low-cost payments and, over time, drains the fee-payer wallet.\n\nThis issue affects mpp: from 0.2.0 before 0.6.0.","status":"published","published":"2026-07-17T12:31:29Z","modified":"2026-07-17T12:31:29Z","cvss":[{"version":"4.0","score":8.3,"vector":"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"high"}],"cwes":["CWE-1284"],"updated_at":"2026-11-02T15:09:35.141236Z"}],"nvd":[{"id":"CVE-2026-59694","description":"Improper Validation of Specified Quantity in Input in ZenHive mpp allows an unauthenticated remote client to inflate the fee-payer's gas cost per payment by a large multiplier, degrading the sponsor's operating margin.\n\nWhen the mpp Elixir library is configured as fee payer (fee_payer: true), MPP.Tempo.Transaction.cosign_fee_payer/3 re-signs the client-supplied base fields of the 0x76 AASigned envelope verbatim, including the EIP-2930 access list, without validating its length or contents. EIP-2930 access list entries incur intrinsic gas (~2,400 gas per address, plus 1,900 gas per storage key) charged before any opcode executes, regardless of whether the listed addresses are ever touched. A malicious client submits a valid transferWithMemo call alongside a large number of fabricated access-list entries. The server co-signs and broadcasts the transaction. The intended transfer executes normally, but the fee-payer wallet pays a large multiple of the expected gas cost with no corresponding on-chain work.\n\nAt the maintainer's default of 137 access-list entries (fitting within Bandit's 10,000-byte per-header-field limit) and 100 Gwei max_fee_per_gas, per-payment gas cost rises from ~51,287 to ~380,087 gas, a 7.4x multiplier. Sustained abuse destroys the sponsor's operating margin on low-cost payments and, over time, drains the fee-payer wallet.\n\nThis issue affects mpp: from 0.2.0 before 0.6.0.","status":"published","published":"2026-07-17T11:17:13.96Z","modified":"2026-10-24T20:10:00.137Z","cvss":[{"version":"4.0","score":8.3,"vector":"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"high","assessor":"secondary"}],"cwes":["CWE-1284"],"updated_at":"2026-11-02T14:12:30.250437Z"}],"osv":[{"id":"CVE-2026-59694","title":"Unbounded access list in mpp Tempo fee-payer inflates gas cost per payment","description":"Improper Validation of Specified Quantity in Input in ZenHive mpp allows an unauthenticated remote client to inflate the fee-payer's gas cost per payment by a large multiplier, degrading the sponsor's operating margin.\n\nWhen the mpp Elixir library is configured as fee payer (fee_payer: true), MPP.Tempo.Transaction.cosign_fee_payer/3 re-signs the client-supplied base fields of the 0x76 AASigned envelope verbatim, including the EIP-2930 access list, without validating its length or contents. EIP-2930 access list entries incur intrinsic gas (~2,400 gas per address, plus 1,900 gas per storage key) charged before any opcode executes, regardless of whether the listed addresses are ever touched. A malicious client submits a valid transferWithMemo call alongside a large number of fabricated access-list entries. The server co-signs and broadcasts the transaction. The intended transfer executes normally, but the fee-payer wallet pays a large multiple of the expected gas cost with no corresponding on-chain work.\n\nAt the maintainer's default of 137 access-list entries (fitting within Bandit's 10,000-byte per-header-field limit) and 100 Gwei max_fee_per_gas, per-payment gas cost rises from ~51,287 to ~380,087 gas, a 7.4x multiplier. Sustained abuse destroys the sponsor's operating margin on low-cost payments and, over time, drains the fee-payer wallet.\n\nThis issue affects mpp: from 0.2.0 before 0.6.0.","status":"published","published":"2026-07-17T10:11:49.192Z","modified":"2026-10-28T02:30:22.493209922Z","cvss":[{"version":"4.0","score":8.3,"vector":"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","level":"high"}],"cwes":["CWE-1284"],"updated_at":"2026-11-02T15:45:12.496548Z"},{"id":"EEF-CVE-2026-59694","title":"Unbounded access list in mpp Tempo fee-payer inflates gas cost per payment","description":"## 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 payment by a large multiplier, degrading the sponsor's operating margin.\n\nWhen the mpp Elixir library is configured as fee payer (fee\\_payer: true), MPP.Tempo.Transaction.cosign\\_fee\\_payer/3 re-signs the client-supplied base fields of the 0x76 AASigned envelope verbatim, including the EIP-2930 access list, without validating its length or contents. EIP-2930 access list entries incur intrinsic gas (~2,400 gas per address, plus 1,900 gas per storage key) charged before any opcode executes, regardless of whether the listed addresses are ever touched. A malicious client submits a valid transferWithMemo call alongside a large number of fabricated access-list entries. The server co-signs and broadcasts the transaction. The intended transfer executes normally, but the fee-payer wallet pays a large multiple of the expected gas cost with no corresponding on-chain work.\n\nAt the maintainer's default of 137 access-list entries (fitting within Bandit's 10,000-byte per-header-field limit) and 100 Gwei max\\_fee\\_per\\_gas, per-payment gas cost rises from ~51,287 to ~380,087 gas, a 7.4x multiplier. Sustained abuse destroys the sponsor's operating margin on low-cost payments and, over time, drains the fee-payer wallet.\n\nThis issue affects mpp: from 0.2.0 before 0.6.0.\n\n## Configurations\n\nThe vulnerable code path is only reachable when the MPP.Methods.Tempo method is configured with fee\\_payer: true (server-side gas sponsorship). Default deployments with fee\\_payer: false are not affected, since the client pays for gas out of its own wallet.","status":"published","published":"2026-07-17T10:11:49.192Z","modified":"2026-09-08T03:30:04.04006683Z","cvss":[{"version":"4.0","score":8.3,"vector":"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","level":"high"}],"cwes":["CWE-1284"],"updated_at":"2026-11-02T15:46:33.520522Z"},{"id":"GHSA-qpxh-ff8m-c62v","title":"mpp vulnerable to Gas Draining with access list","description":"### Details\nWhen the server acts as the fee_payer, `mpp` Elixir 0.4.0 copies the client-supplied EIP-2930 access list verbatim into the cosigned fee-payer transaction. In `cosign_fee_payer`, the server re-signs the raw `base_fields` (index 5 of the 0x76 AASigned envelope) without inspecting the access list field, which is part of the signed payload.\n\nAccess list gas is charged **intrinsically** — before any opcode executes — regardless of whether the listed addresses are ever touched.\n\nAn attacker submits a valid `transferWithMemo` alongside fabricated address-only access list entries. The server validates calldata and amount but never inspects `access_list` length. It cosigns and broadcasts a transaction that costs the fee-payer wallet `N × 2,400` extra gas per request with no corresponding work performed on-chain.\n\nAt the default of 137 entries and 100 Gwei `max_fee_per_gas`, this inflates the fee-payer cost from the normal ~51,287 gas to ~380,087 gas — a **7.4× multiplier** — while staying within Bandit's default 10,000-byte per-header-field limit (verified empirically).\n\n### PoC\nThe PoC is provided below. It is configured to reproduce the attack on Tempo Moderate testnet within a Docker environment. Download the PoC and run:\n```bash\nunzip mpp_elixir_PoC.zip\ncd mpp_elixir\ndocker build -t mpp-elixir-access-list .\ndocker run --rm mpp-elixir-access-list\n``` \nThere are more details in `mpp_elixir/README.md`\n\n### Impact\nA malicious client can force the server to pay ~**7.4x** the normal transaction fee. This dramatically increases operational costs and completely destroys the profit margin on low-cost items.","status":"published","published":"2026-09-25T21:45:16Z","modified":"2026-09-25T23:00:31.297255816Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N","level":"medium"}],"cwes":["CWE-20"],"updated_at":"2026-11-02T15:46:54.760124Z"}]}}