GHSA-c8w6-x74f-vmg3: Zebra rpc Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-c8w6-x74f-vmg3",
  "modified" : "2026-07-02T19:37:58Z",
  "published" : "2026-07-02T19:37:58Z",
  "aliases" : [ ],
  "summary" : "zebrad vulnerable to full node denial of service via crafted Sapling receiver in z_listunifiedreceivers",
  "details" : "### Am I affected\n\nYou are affected if:\n\n1. You run `zebrad` up to and including `v4.4.1`.\n2. Your `zebrad.toml` sets `rpc.listen_addr` to a TCP address (RPC server is enabled).\n3. An attacker can authenticate to the RPC endpoint. With the default `enable_cookie_auth = true`, this requires the attacker to read the `.cookie` file (typically local access). With `enable_cookie_auth = false`, any network client reaching the RPC port can trigger it.\n\n### Summary\n\nThe `z_listunifiedreceivers` RPC handler panics when processing a structurally valid Unified Address whose Sapling receiver carries 43 bytes that fail cryptographic validation (`sapling_crypto::PaymentAddress::from_bytes` returns `None` for non-subgroup Jubjub points). The handler calls `.expect(\"using data already decoded as valid\")` on the fallible result. Because Zebra's release profile sets `panic = \"abort\"`, the panic terminates the entire node process, not just the RPC task.\n\n### Details\n\n`zcash_address::unified::Encoding::decode` validates only the structural envelope of a Unified Address (F4Jumble, bech32m, typecode ordering, 43-byte length for Sapling). It does not validate that the embedded `pk_d` is a valid Jubjub subgroup point or that the diversifier produces a valid `g_d` preimage.\n\nAt `zebra-rpc/src/methods.rs:2893`, the handler calls `Address::try_from_sapling(network, data)`, which delegates to `sapling_crypto::PaymentAddress::from_bytes`. When `from_bytes` returns `None` (most random 32-byte strings fail the subgroup check), the `.expect()` fires and the process aborts.\n\nThe same crate already handles this correctly in `try_from_unified` at `zebra-chain/src/primitives/address.rs:99-110`, which returns `Err` when `from_bytes` fails. The vulnerable code path bypasses this validated route.\n\n### Patches\n\nzebra-rpc 8.0.0 and zebrad 4.5.0.\n\nReplace `.expect()` with `.map_err(|e| ErrorObject::owned(...))` for proper error propagation, or route through the existing `try_from_unified` path which already handles this case correctly.\n\n### Workarounds\n\n- Disable the RPC server by removing `rpc.listen_addr` from `zebrad.toml`.\n- Ensure `enable_cookie_auth = true` (the default) and restrict filesystem access to the `.cookie` file.\n- Place a reverse proxy in front of the RPC port that rejects `z_listunifiedreceivers` calls with untrusted address parameters.\n\n### Impact\n\nA single authenticated RPC request terminates the `zebrad` process. The attack is repeatable on restart (the same request triggers the same abort), allowing an attacker to keep the node down indefinitely until the request is filtered upstream. Operators using `lightwalletd` backends, Zaino indexers, or mining pool infrastructure that forward RPC calls to `zebrad` may be exposed if the forwarding path passes through `z_listunifiedreceivers`.\n\n### Credit\n\nReported by `@robustfengbin` via a private GitHub Security Advisory submission.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "zebra-rpc"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "8.0.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 7.0.0"
    }
  }, {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "zebrad"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.5.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.4.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-c8w6-x74f-vmg3"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/ZcashFoundation/zebra"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ZcashFoundation/zebra/blob/d4cd662c716382f6397d2a730148025a1ca79fec/Cargo.toml#L305"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ZcashFoundation/zebra/blob/d4cd662c716382f6397d2a730148025a1ca79fec/zebra-rpc/src/methods.rs#L2867-L2914"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20", "CWE-248", "CWE-617", "CWE-754" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-02T19:37:58Z",
    "nvd_published_at" : null
  }
}