CVE-2026-82751 Unbounded key authorization in mpp Tempo fee-payer sponsorship inflates gas cost and sponsors access-key provisioning
Attackers can inflate sponsor gas costs and provision unauthorized access keys by bypassing validation in the Tempo fee-payer policy.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-82751?
CVE-2026-82751 is a high-severity vulnerability in ZenHive mpp, published on 6 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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 sponsored payment by a large multiplier and to have the sponsor pay for provisioning an access key on the client's own account.
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 does not check whether the envelope carries the optional key_authorization field. A client can attach a fully signed key authorization, provisioning a new access key with token spending limits on its own account, alongside the normal payment call. The key and each limit entry are persistent storage writes billed as intrinsic gas to the sponsor, bounded only by the gas_limit ceiling. At the reporter's default of one key with three token limits the sponsored cost rises from about 46,587 gas to about 1,808,700 gas, and the client keeps a valid access key it paid nothing for.
This issue affects mpp: from 0.2.0 before 0.16.1.
Weakness: CWE-1284
Which versions are affected by CVE-2026-82751?
1 open source package ship an affected version, including mpp.
| Package | Affected | Fixed in |
|---|---|---|
mpp Hex | From 0.2.0 | 0.16.1 |
How do I fix CVE-2026-82751?
Upgrade mpp to 0.16.1 or later.
Is CVE-2026-82751 being exploited?
There is no known exploitation of CVE-2026-82751 in the wild and no public exploit code.
Sources
Also known as EEF-CVE-2026-82751, GHSA-6fjm-7mv9-c325, GHSA-rpwj-vrf7-4x36.