Bug 2567537 (CVE-2026-61618)

Summary: CVE-2026-61618 snark-verifier: snark-verifier: Denial of Service via non-canonical accumulator limb decoding
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in snark-verifier. Accumulator limbs are decoded without consistently enforcing canonical bounds before reconstructing elliptic-curve coordinates. A remote attacker can exploit this flaw by submitting proofs with non-canonical encodings, causing the native verifier to panic and crash rather than returning a standard verification error, leading to a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-11-05 22:05:41 UTC 
SNARK Verifier is a generic (S)NARK verifier. Prior to 0.2.5, KZG accumulator public-instance limbs are decoded without consistently enforcing canonical limb bounds before elliptic-curve coordinate reconstruction. `PlonkProof::read` selects scalars using `accumulator_indices` and passes them to `AccumulatorEncoding::from_repr`. For the EVM loader, `LimbsEncoding::from_repr` forwards them to `EvmLoader::ec_point_from_limbs` in `snark-verifier/src/loader/evm/loader.rs`, where `shl` and `add` reconstruct coordinates before `validate_ec_point` checks the resulting affine point rather than the original limb bounds. The related native path in `snark-verifier/src/pcs/kzg/accumulator.rs` can reach assertion- or unwrap-based decoding and panic instead of returning a verification error. This allows noncanonical encodings at the verifier boundary and can crash the native verifier. Standard SDK aggregation circuits are expected to constrain accumulator limbs before this boundary, which limits practical exploitability. This issue is fixed in version 0.2.5.