Am I affected
You are affected if:
- You run
zebrad up to and including v4.4.1.
- Your node listens on the default
[::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
- Your node is synced near the chain tip (the expected production state for any node participating in the network).
Summary
An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.
The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.
Details
On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).
The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.
After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.
The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.
Patches
Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.
Workarounds
Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.
Impact
A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.
Credit
Reported by @Haxatron.
References
Haxatron Reporter
oxarbitrage Remediation developer
mpguerra Coordinator
Am I affected
You are affected if:
zebradup to and includingv4.4.1.[::]address on a Linux host (the standard deployment configuration —net.ipv6.bindv6only=0is the default on all common Linux distributions).Summary
An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.
The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via
MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sendingMetaAddrChange::UpdateMisbehaviorto the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, andpanic = "abort"terminates the process.Details
On Linux with
net.ipv6.bindv6only=0, an IPv4 connection accepted by a[::]listener is represented internally as an IPv4-mapped IPv6 socket address (e.g.,::ffff:127.0.0.1:8233). Zebra'scanonical_peer_addrhelper converts these to plain IPv4 (e.g.,127.0.0.1:8233).The handshake path uses
MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration usesconnected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel toMetaAddrChange::UpdateMisbehavior, which does not canonicalize.After the 30-second misbehavior batch flush,
AddressBook::updateretrieves the canonical IPv4 entry butMetaAddrChange::apply_to_meta_addrasserts thatprevious.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.
Patches
Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new
MetaAddr::new_misbehaviorconstructor that appliescanonical_peer_addrbefore creating theUpdateMisbehaviorchange.Workarounds
Configuring
listen_addrto an IPv4-only address (e.g.,0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, settingnet.ipv6.bindv6only=1on Linux prevents dual-stack acceptance.Impact
A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.
Credit
Reported by
@Haxatron.References