fix: cap WebAuthn key_id at 1023 bytes at registration - #121
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fix: cap WebAuthn key_id at 1023 bytes at registration#121alberto-crossmint wants to merge 1 commit into
alberto-crossmint wants to merge 1 commit into
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WebauthnSigner.key_id is declared as unbounded `Bytes`, so an arbitrary caller could register a signer whose credential ID is megabytes long. Persistent storage rent scales with entry size, signature proof payloads grow accordingly, and real-world WebAuthn CredentialIDs fit comfortably under the FIDO2/CTAP2 cap of 1023 bytes — typically ≤ 128 bytes. Reject add_signer / update_signer when the Webauthn key_id exceeds 1023 bytes, using the existing InvalidPolicy error code.
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Summary
WebauthnSigner.key_idis typed as unboundedsoroban_sdk::Bytes. Nothing inadd_signer/update_signerenforced a length cap, so a caller could register a credential ID of arbitrary size. That inflates:__check_auth, sinceSignerProof::Webauthncarries thekey_id-indexed map entry.The FIDO2/CTAP2 spec caps
CredentialIDat 1023 bytes, and real-world authenticators produce IDs well under that (typically ≤ 128). There is no legitimate reason to exceed the cap.This PR adds a single bounds check at signer registration (
add_signerandupdate_signer), surfacingInvalidPolicyfor anything over 1023 bytes.Test plan
test_webauthn_oversize_key_id_rejected— 1024-bytekey_id→Err(InvalidPolicy).test_webauthn_max_size_key_id_accepted— exactly 1023 bytes → accepted.Risk
Minimal. All observed
WebauthnSigneruses in this repo have shortkey_idvalues (test fixtures use 18 bytes, migration tests preserve v1 values which were similarly short). If a production account somehow holds a >1023-bytekey_id,__check_authis unaffected — only futureadd_signer/update_signercalls are gated.