Security fixes are applied to the latest release on main / the newest v* tag.

• Daemon TLS certificates are auto-generated and stored under ~/.config/quiksync/ (override with $QUIKSYNC_CONFIG).
• Clients pin the server certificate fingerprint on first connect (TOFU). A later fingerprint mismatch fails the dial. First connect silently pins — verify the host on first use.
• --insecure skips pin verification and is intended for labs only.
• Serve defaults to 127.0.0.1:4242 and requires a shared --auth-token (or QUIKSYNC_AUTH_TOKEN). Use --allow-no-auth only for labs. Non-loopback listen addresses always require a token.
• Concurrent QUIC streams are capped to limit resource exhaustion.
• Protocol Hello negotiates capability bits (including sparse ReuseChunk). Older remotes without reuse fall back to full-wire chunk send.

• Daemon filesystem access is confined to serve --root via path joining that rejects .., absolute paths, empty/." targets, and symlink escapes outside the root.
• Client Hello.Root cannot override the server root for the daemon.
• Decompress (zstd/lz4) output is capped per chunk to prevent decompression bombs.

• Credentials come from the AWS SDK default chain (env, shared config, instance role). Prefer least-privilege IAM scoped to the destination bucket/prefix.
• Use --s3-endpoint only with trusted S3-compatible endpoints (MinIO/R2). Prefer TLS endpoints in production.
• Prefer bucket default encryption (SSE-S3 / SSE-KMS). QuikSync does not yet client-encrypt object payloads.
• --delete permanently removes objects under the destination prefix (plus signature sidecars).
• After a successful object put, a failed signature-sidecar write fails the commit (object may already exist; the next successful sync repairs the sidecar).

• Mounted NFS paths use the local transport; trust the mount and export options (root squashing, sec=).
• Native nfs:// is experimental (NFSv3 + AUTH_SYS only, unencrypted) and expands the network attack surface versus a kernel mount. Prefer mounts for production. Writes use staged temp files + NFSv3 RENAME; mode/mtime are not applied. Custom ports are rejected (portmapper-based dial).

• Payload objects are content-addressed; receivers reject bytes that do not match the digest (poison objects fail closed).
• Manifests and leases on a shared writable prefix are a trusted-peer channel — anyone who can write the mid prefix can publish jobs. Isolate prefixes per pair with IAM or share ACLs.
• Job IDs are sanitized before path construction (no .. or separators), so relay state stays under .quiksync/relay/<job>/. Use one sender per job id.
• Manifests are validated (schema, job id, relative paths, chunk coverage) before materialize.
• --signal quiksync://… / SSH is wakeup-only (process-local waiter on the peer daemon); the receiver always re-reads and verifies store state. Signal compromise must not grant data-plane trust.
• Use SSE on the mid bucket; client-side mid-hop encryption is not yet implemented.
• relay gc deletes job objects after ack (or forced TTL); do not point --via at unrelated prefixes.

Please do not open a public issue for security problems that could be exploited.

Prefer:

1. GitHub Private vulnerability reporting on shaneburrell/quiksync, or
2. Contact via github.com/shaneburrell

Include QuikSync version, OS, reproduction steps, and impact. You should receive an acknowledgment when possible; coordinated disclosure is appreciated.