CVE-2026-88255

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.

• https://github.com/ZenHive/mpp/commit/e12bd4a1cea2e97c2a01fc059c48e5594a7b4a43
• https://github.com/ZenHive/mpp/commit/f8904666061fbab695874856d8fcd02c471dfe1b
• https://github.com/ZenHive/mpp/security/advisories/GHSA-8x7x-5j8g-8hcx

• https://cna.erlef.org/cves/CVE-2026-88255.html
• https://github.com/ZenHive/mpp/commit/e12bd4a1cea2e97c2a01fc059c48e5594a7b4a43
• https://github.com/ZenHive/mpp/commit/f8904666061fbab695874856d8fcd02c471dfe1b
• https://github.com/ZenHive/mpp/security/advisories/GHSA-8x7x-5j8g-8hcx
• https://osv.dev/vulnerability/EEF-CVE-2026-88255