GHSA-452v-w3gx-72wg Zebra has rk Identity Point Panic in Transaction Verification

• crates.io zebrad: < 4.3.1 → fixed in 4.3.1 • crates.io zebra-chain: < 6.0.2 → fixed in 6.0.2

rk Identity Point Panic in Transaction Verification Summary Orchard transactions contain a `rk` field which is a randomized validating key and also an elliptic curve point. The Zcash specification allows the field to be the identity (a "zero" value), however, the `orchard` crate which is used to verify Orchard proofs would panic when fed a `rk` with the identity value. Thus an attacker could send a crafted transaction that would make a Zebra node crash. Severity Critical - This is a Denial of Service Vulnerability that could allow an attacker to crash Zebra nodes. Affected Versions All Zebra versions prior to version 4.3.1. Description The vulnerability exists in the `circuits.rs` file of the `orchard` crate; it attempts to get the coordinates of the `rk` value and calls `unwrap()` on the results, which causes a panic if `rk` is the identity. Zebra parses `rk` as a byte vector; it creates an Orchard "bundle" using the `orchard` crate and then calls the same crate to verify it, triggering the panic. An attacker could exploit this by: 1. Creating a transaction with a identity `rk` 2. Submitting it to a Zebra node, making it crash Impact Denial of Service • Attack Vector: Network. • Effect: Node crash. • Scope: Any impacted Zebra node. Fixed Versions This issue is fixed in Zebra 4.3.1. The fix was agreed with `zcashd` developers (which has the same issue) to not allow the identity `rk` anymore and change the specification as such. Zebra now does this when parsing a transaction. This was deemed easier than fixing the issue in `orchard`, which would make the bug public before the nodes could be patched. Mitigation Users should upgrade to Zebra 4.3.1 or later immediately. There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to denial of service. Credits Thanks to Alex “Scalar” Sol for finding and reporting the issue.