EEF-CVE-2026-88255 CVE-2026-88255 GHSA-8x7x-5j8g-8hcx
mpp Tempo keys its pre-broadcast dedup reserve on the caller-supplied transaction encoding, so a re-encoded signed transaction reserves a second slot
- 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-1289 Improper Validation of Unsafe Equivalence in Input
- Fix
0.16.2- Upgrade mpp to this version or later
Description
Summary
Improper Validation of Unsafe Equivalence in Input in ZenHive mpp allows an unauthenticated remote client to pass the Tempo duplicate-submission gate twice with one signed transaction.
MPP.Methods.Tempo reserves the pre-broadcast dedup slot on the caller-supplied hex in reserve_hash_atomic/2, keyed through store_key/1 on tx.raw rather than on a canonical form of the transaction. The deserializer stores the caller's hex verbatim and accepts both recovery-id encodings, so one signed transaction submitted once with v=27 and once with v=0 yields two distinct reserve keys, and both pass the reserve and reach the broadcast path. The plug-level credential replay store is deliberately carved out for tempo in lib/mpp/replay.ex, leaving this reserve as the only gate, and the post-broadcast mark writes the canonical hash key that the raw-keyed reserve never reads.
What the duplicate submission yields depends on the node: a nonce-reuse rejection fails closed, while a node that answers with the canonical hash for an already-known transaction returns a second valid Payment-Receipt for a single on-chain payment.
This issue affects mpp: from 0.2.0 before 0.16.2.
Impact
A client re-encodes the recovery id of a transaction it has already submitted and presents it again. The duplicate passes the only duplicate-submission gate the Tempo method has, and against a node that answers with the canonical hash for an already-known transaction the client is issued a second Payment-Receipt for one on-chain payment.
Configurations
Reachable when MPP.Methods.Tempo broadcasts a type="transaction" credential with a dedup store in place. From mpp 0.7.0 the dedup store is on by default (the app-started MPP.Tempo.ConCacheStore; opt out with store: false), so every default Tempo deployment from 0.7.0 before 0.16.2 is affected. Before 0.7.0 the default store was nil, which runs the library statelessly and provides no application-level replay protection at all, a documented property rather than part of this issue; those versions are affected only where a "store" was configured explicitly in method_config.
Affected versions
Hex
| Package | Vulnerable | Fixed in |
|---|---|---|
| mpp | >= 0.2.0, < 0.16.2 |
0.16.2 |
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 → 0.16.2
- mix
{:mpp, "~> 0.16.2"} # 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:L/VA:N/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)
- Low
- Availability (vulnerable system)
- None
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None
Weakness
CWE-1289: Improper Validation of Unsafe Equivalence in Input
The product receives an input value that is used as a resource identifier or other type of reference, but it does not validate or incorrectly validates that the input is equivalent to a potentially-unsafe value.
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-2026-89186 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-2026-82750 Unbounded EIP-7702 authorization list in mpp Tempo fee-payer sponsorship inflates gas cost and sponsors account delegation | 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
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