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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

Quick assessment

Affected
ZenHive mpp
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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-suppl

CVSS 6.3 · Medium
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I. Basic Information for CVE-2026-88255

Vulnerability Information
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Vulnerability Title
mpp Tempo keys its pre-broadcast dedup reserve on the caller-supplied transaction encoding, so a re-encoded signed transaction reserves a second slot
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1289
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
ZenHive mpp 0.2.0 ~ 0.16.2 cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*
ZenHive mpp f8904666061fbab695874856d8fcd02c471dfe1b ~ e12bd4a1cea2e97c2a01fc059c48e5594a7b4a43 cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*

II. Public POCs for CVE-2026-88255

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III. Intelligence Information for CVE-2026-88255

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Patches & Fixes for CVE-2026-88255 (1)

Other References for CVE-2026-88255 (3)

IV. Related Vulnerabilities

Same product: mpp
Same vendor: ZenHive
Same weakness: CWE-1289

V. Comments for CVE-2026-88255

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