EEF-CVE-2026-82750 CVE-2026-82750 GHSA-5qrp-r24c-w6jr
Unbounded EIP-7702 authorization list in mpp Tempo fee-payer sponsorship inflates gas cost and sponsors account delegation
- Severity
- 0.0 / 10
- Unknown · CVSS 4.0
- Exploit chance (EPSS)
- 0.52%
- Chance of exploitation in the next 30 days. Higher than 44.44% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-1284 Improper Validation of Specified Quantity in Input
- Fix
0.16.1- Upgrade mpp to this version or later
Description
Summary
Improper 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.
When 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.
This issue affects mpp: from 0.2.0 before 0.16.1.
Workarounds
Disable 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.
Configurations
Only 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.
Affected versions
Hex
| Package | Vulnerable | Fixed in |
|---|---|---|
| mpp | >= 0.2.0, < 0.16.1 |
0.16.1 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
mpp Hex → 0.16.1
- mix
{:mpp, "~> 0.16.1"} # then: mix deps.update mpp
Severity breakdown
CVSS 4.0 0.0
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
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- Present
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- None
- Integrity (vulnerable system)
- High
- Availability (vulnerable system)
- Low
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None
Weakness
CWE-1284: Improper Validation of Specified Quantity in Input
The product receives input that is expected to specify a quantity (such as size or length), but it does not validate or incorrectly validates that the quantity has the required properties.
How to prevent it
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
References
Advisories
Fixes and patches
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| EEF-CVE-2026-87119 mpp Tempo subscription key authorization is not bound to the issuing challenge, allowing a captured activation credential to be replayed | Not rated yet | Also affects mpp |
| EEF-CVE-2026-89420 Session voucher adding no new funds is accepted without a charge in mpp, serving paid resources for free | Not rated yet | Also affects mpp |
| EEF-CVE-2026-88255 mpp Tempo keys its pre-broadcast dedup reserve on the caller-supplied transaction encoding, so a re-encoded signed transaction reserves a second slot | Not rated yet | Also affects mpp |
| EEF-CVE-2026-89186 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 | Not rated yet | Also affects mpp |
| EEF-CVE-2026-82751 Unbounded key authorization in mpp Tempo fee-payer sponsorship inflates gas cost and sponsors access-key provisioning | Not rated yet | Also affects mpp |
| EEF-CVE-2026-67581 On-chain transfer proof is not single-use in mpp EVM payment method, enabling cross-challenge replay | High | Also affects mpp |
| EEF-CVE-2026-73541 Tempo fee sponsorship in mpp bounds each transaction but not aggregate exposure, allowing concurrent sponsor-wallet drain | High | Also affects mpp |
| EEF-CVE-2026-73136 Static memo configuration in mpp Tempo disables per-challenge attribution binding, enabling third-party replay | High | Also affects mpp |
Credits: E.FU, Jonatan Männchen / EEF, Kian Kai Ang
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