GHSA-qv2r-v3mx-f4pf: zebrad has full node denial of service via non-ASCII LongPollId in getblocktemplate

Am I affected You are affected if: 1. You run zebrad up to and including v4.4.1. 2. Your zebrad.toml sets rpc.listen_addr to a TCP address (RPC server is enabled). 3. An attacker can authenticate to the RPC endpoint. With the default enable_cookie_auth = true, this requires the attacker to read the .cookie file. With enable_cookie_auth = false, any network client reaching the RPC port can trigger it. Summary The getblocktemplate RPC handler panics when parsing a LongPollId parameter that contains non-ASCII (multi-byte UTF-8) characters. The handler performs byte-index string slicing on the user-supplied string, which panics in Rust when a byte index falls within a multi-byte character boundary. Because Zebra's release profile sets panic = "abort", the panic terminates the entire node process. Details The getblocktemplate handler receives a user-supplied LongPollId string and slices it at fixed byte offsets to extract the encoded tip hash and tip height. When the string contains multi-byte UTF-8 characters, a byte-index slice can land in the middle of a character, causing Rust's str indexing to panic with "byte index is not a char boundary." Under the panic = "abort" release profile, this panic terminates the entire zebrad process rather than just the RPC task. Patches zebra-rpc 8.0.0 and zebrad 4.5.0. Replace byte-index string slicing with character-aware parsing or validate that the LongPollId string contains only ASCII characters before slicing. Workarounds - Disable the RPC server by removing rpc.listen_addr from zebrad.toml. - Ensure enable_cookie_auth = true (the default) and restrict filesystem access to the .cookie file. - Place a reverse proxy in front of the RPC port that validates LongPollId parameters are ASCII-only before forwarding. Impact A single authenticated RPC request terminates the zebrad process. Same impact profile as GHSA-c8w6-x74f-vmg3: repeatable on restart, af