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0xCERT Security Advisory 0xCERT-2026-0182
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Advisory-ID:  0xCERT-2026-0182
Severity:     High
Published:    2026-09-28T17:17:49.547Z
Updated:      2026-10-08T22:46:38.986Z
Chains:       Ethereum
URL:          https://www.0xcert.com/advisory/0xCERT-2026-0182

Title: CVE-2026-48100: Payy

Summary
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Payy is an Ethereum L2 zk-rollup for privacy preserving and regulatory compliant transactions. Prior to version 1.3.0, agg_agg forwards the compacted message stream from its inner proofs into a public messages: [Field; 1000] array, but it never checks that the unused tail of the outer array is zero. A registered prover can build a valid agg_final proof for an approved rollup block while inserting an extra burn message after the real messages. RollupV1.verifyRollup() then parses that public input as a normal burn and transfers USDC from the rollup contract to the attacker. This is a severe cir…

Details
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Summary
Payy is an Ethereum L2 zk-rollup for privacy preserving and regulatory compliant transactions. Prior to version 1.3.0, agg_agg forwards the compacted message stream from its inner proofs into a public messages: [Field; 1000] array, but it never checks that the unused tail of the outer array is zero. A registered prover can build a valid agg_final proof for an approved rollup block while inserting an extra burn message after the real messages. RollupV1.verifyRollup() then parses that public input as a normal burn and transfers USDC from the rollup contract to the attacker. This is a severe circuit soundness failure: the proof system accepts a public statement whose messages array is not fully derived from the verified inner proofs. On the current deployment, verifyRollup() is restricted to the existing allowlisted prover, so a fresh public caller cannot submit the invalid proof directly. That gate limits who can reach L1 today; it does not make the circuit statement sound. The issue becomes permissionless under the prover model described in the Payy whitepaper. Section 3.3.2 states: "To join as a prover, the prover is required to submit a small stake", and Section 3.3.1 states that if a prover fails to submit, "other nodes can submit the block proof instead." In that model, an attacker only needs to become a registered prover and use public validator approval data for an already approved block. This issue has been patched in version 1.3.0.

Severity
High (CVSS 8.7), as scored by NVD.

Weakness
- - CWE-349

Recommended actions
- - Check whether you run or depend on the affected component and version
- - Apply the vendor's fix or mitigation from the references below

Source & attribution
This 0xCERT advisory summarises CVE-2026-48100 from the U.S. National Vulnerability Database: https://nvd.nist.gov/vuln/detail/CVE-2026-48100. Details may change; refer to the original source for the authoritative record.

References
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- - https://nvd.nist.gov/vuln/detail/CVE-2026-48100
- - https://github.com/polybase/payy/security/advisories/GHSA-fhxc-63vg-9gwr
- - https://github.com/polybase/payy/security/advisories/GHSA-fhxc-63vg-9gwr

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