fix: reject zero sessionId in verifySession - #882
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The id_commitment circuit constraint is a disjunction: it holds when the commitment equals H(DS_C, mt_index, r) or when it is zero. Zero is the "no session" sentinel every Uniqueness Proof uses, and it is satisfiable by any World ID regardless of mt_index. A session record left at zero can therefore be satisfied by an arbitrary World ID with a patched authenticator, voiding the same user+RP continuity guarantee. V2 is released and immutable, so the check lands in a new WorldIDVerifierV3 that overrides verifySession. Existing deployments are remediated by upgrading the proxy to V3. Reported via HackerOne #3912490. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
…3-reject-zero-session
Follows the error moving onto the V2 interface. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Dzejkop
reviewed
Aug 4, 2026
Dzejkop
reviewed
Aug 4, 2026
The fuzz test forces the 0x02 prefix and covers the same assertion, so the fixed-action case adds no coverage. Its rationale comment moves to the fuzz test. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
paolodamico
previously approved these changes
Aug 5, 2026
Prefixes the file names so V3 is not mistaken for a shipped version. Drop the prefix once it ships. Contract and interface names are unchanged, so the deployed identity and ABI are unaffected. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Dzejkop
approved these changes
Aug 5, 2026
paolodamico
approved these changes
Aug 5, 2026
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verifySessionacceptssessionId == 0, which is the circuit's "no session" sentinel and is satisfiable by any World ID. A session record left at zero can therefore be satisfied by an arbitrary World ID, voiding the "same user + RP pair across requests" continuity guarantee thatverifySessionis meant to provide.Adds
WorldIDVerifierV3, which overridesverifySessionto reject a zerosessionId. Purely additive — three new files, no existing file is modified.Reported via HackerOne #3912490.
Why the sentinel is universally satisfiable
circom/client_side_proofs/oprf_nullifier.circom:183constrains the commitment as a disjunction:It is satisfied either when
id_commitment == H(DS_C, mt_index, id_commitment_r)or whenid_commitment == 0. The zero branch places no constraint onmt_index, so it is not merely "unbound" — it is provable by any identity in the tree. Every Uniqueness Proof uses that branch legitimately, so the sentinel cannot be removed from the circuit; the verifier has to reject it at the boundary instead.