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Fencer Intel
medium 6.3

CVE-2026-88255 json

mpp Tempo keys its pre-broadcast dedup reserve on the caller-supplied transaction encoding, so a re-encoded signed transaction reserves a second slot

published 2mo ago modified last mo. also EEF-CVE-2026-88255 , EUVD-2026-80256 , GHSA-8x7x-5j8g-8hcx

cvss
6.3
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 44%
public exploits
0
none known

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.

Patch / fix

  • hex mpp 0.16.2
  • ZenHive mpp 0.16.2

Is CVE-2026-88255 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
last mo.

Exploit prediction

0.52% chance of exploitation in the next 30 days, higher than 44% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 4.0 6.3 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
CNA 4.0 6.3 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/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

Affected packages

ecosystem package affected fixed in
hex mpp
>=0.2.0, <0.16.2
0.16.2

Affected products

  • ZenHive mpp

Classification

Weakness
  • CWE-1289 Improper Validation of Unsafe Equivalence in Input

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of ZenHive/mpp published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.