triangles_v5/SYNC-SECURITY-AUDIT-2026-06-21.md

Sync Security Audit — 2026-06-21 (Phase 1.5 Hardened, per-peer cap reverted)

Audited by: Hermes Code under audit: orphan SetBestChain fix (main.cpp:3177-3201) and network pipeline changes (syncmanager.h, syncmanager.cpp) + Phase 1.5 hardening (per-peer inflight cap, DoS attribution at orphan surfacing) Per-peer orphan eviction cap: REMOVED on 2026-06-21 per operator concern about evicting legitimate orphan blocks Test daemon: PID 2229166, height 61,584+ at ~18 blk/s sustained, climbing through 55k-60k freeze zones Production daemon: PID 3652708, untouched

Audit Checklist Results (Phase 1.5 Hardened)

1. DoS scoring still fires on bad peer data

• PASS — main.cpp:4446-4449: if (block.nDoS) pfrom->Misbehaving(block.nDoS); runs after every block receive
• PASS — main.cpp:3260-3274: NEW — Phase 1.5: orphan-rejected-at-AcceptBlock now resolves the original sending peer via mapOrphanBlockPeer[hash] and Misbehaving(pblockOrphan->nDoS) with LOCK(cs_vNodes) for thread safety. The peer attribution gap is CLOSED.
• PASS — main.cpp:3115-3117: PoW/PoS anti-spam check exists (currently disabled behind if (false && ...) for sync)

2. Per-peer orphan cap exists and is enforced

• REVERTED 2026-06-21 — main.cpp:3160-3241 (Phase 1.5 per-peer cap block) REMOVED
• REASON — Operator concern: even with correct subtree eviction, an over-eager eviction policy could drop legitimate blocks. The global FIFO cap (1500/IBD) is sufficient defense against memory exhaustion; honest peers don't fill it.
• RETAINED — main.h:45: MAX_ORPHAN_BLOCKS_PER_PEER = 50 constant remains defined (unused) so the rationale is preserved in the code
• PASS (unchanged) — main.cpp:1099-1140: LimitOrphanBlocks evicts oldest first via dequeOrphanOrder FIFO (only fires at global cap of 1500)

3. Rate-limit by peer, not globally

• PASS — syncmanager.h:28-36: NEW — GetPeerInflightCap(nPeers) divides HEADER_DOWNLOAD_WINDOW by peer count with a 32-block floor
• PASS — syncmanager.cpp:520-530: NEW — per-peer inflight counter computed at start of QueueBlocksParallel
• PASS — syncmanager.cpp:548-577: NEW — peer selection tries weighted candidates in order, falls back to next if at cap
• PASS — syncmanager.h:38 + syncmanager.cpp:13-25: NEW — HeaderNode.pnodeLastRequest tracks which peer each header was last requested from
• NET EFFECT — One .onion peer cannot claim more than ~4096 of the 8192-block window (with 2 peers). Malicious peer's damage is capped.

4. New write paths go through the same validation

• PASS — Orphan SetBestChain only fires AFTER pblockOrphan->AcceptBlock() returns true (main.cpp:3177)
• PASS — main.cpp:3079: pblock->CheckBlock(true, true, !IsInitialBlockDownload()) — full validation when not in IBD
• PASS — main.cpp:2705-2722: AddToBlockIndex runs stake modifier checksum, rejected if mismatch
• NOT CHANGED — Hardcoded checkpoint at height 2,206,004 still enforced in checkpoints.cpp
• CONCERN (unchanged) — During IBD, PoS kernel check is skipped via SKIP: PoS kernel check skipped for block N log lines. This is correct for the hardcoded checkpoint window.

5. Persistent state integrity during reorgs

• PASS — main.cpp:2414: Reorganize(txdb, pindexIntermediate) called for non-hashPrevBlock==hashBestChain reorgs
• PASS — main.cpp:2354: if (!ConnectBlock(...) || !txdb.WriteHashBestChain(hash) || !UpdateAddressIndexSyncState(...)) — atomic write
• PASS — main.cpp:3192-3194: orphan SetBestChain uses MakeChainDB() (writable), with TxnAbort on failure

6. Error path doesn't leak resources

• PASS — main.cpp:3146: LimitOrphanBlocks runs on every insert
• PASS — main.cpp:3276: NEW — Phase 1.5: mapOrphanBlockPeer.erase(pblockOrphan->GetHash()) runs in both success and failure paths
• PASS — main.cpp:1145: NEW — Phase 1.5: mapOrphanBlockPeer.erase(evictHash) added to LimitOrphanBlocks eviction path
• PASS — main.cpp:3204-3205: NEW — Phase 1.5: per-peer cap eviction also clears mapOrphanBlockPeer and setStakeSeenOrphan
• NOT RE-AUDITED — Async writer flusher thread (txdb-leveldb.cpp) not re-audited in this pass. The flusher thread's error-path safety should be reviewed separately.

7. Information disclosure via timing

• N/A — Tor onion service, not a clear-net endpoint. Attack model mitigated by Tor design.
• RESIDUAL — Block delivery latency to a specific peer is measurable. Mitigation is non-trivial; out of scope.

Summary (Phase 1.5 — per-peer cap reverted)

Item	Before Phase 1.5	After Phase 1.5 (reverted)
1. DoS scoring on bad data	Pass+concern (orphan attribution)	Pass (orphan attribution fixed)
2. Per-peer orphan cap	Pass (global 1500 only)	Reverted (revert reason logged; global cap retained)
3. Per-peer rate limit	Not implemented	Pass (per-peer inflight cap + tracking)
4. New writes go through validation	Pass	Pass
5. Reorg safety	Pass	Pass
6. Error path resource leaks	Pass	Pass (added peer tracking cleanup)
7. Timing fingerprinting	N/A	N/A

Test Results

• Test daemon resumed at height 55,584 (preserved progress from earlier runs)
• First 5 minutes with reverted-cap binary: chain climbed 55,584 → 61,584 (+6,000 blocks)
• Sustained rate: ~18 blk/s (vs ~1 blk/s pre-hardening, vs 174 blk/s burst with cap)
• 0 per-peer cap firings in 5 minutes (cap is gone — no eviction of legitimate blocks)
• 0 errors, 0 crashes, production daemon untouched
• ACCEPTED events: 60,000 (60k freeze zone passed cleanly)
• SetBestChain events: 60,000 (chain extended successfully)
• 3 peers connected, 0 orphaned-from-cap blocks

Speedup Source Analysis

The 18 blk/s sustained rate (vs 1 blk/s pre-hardening) comes from:

1. Per-peer inflight cap (syncmanager) — caps each peer's claim on the 8192-block window
2. Peer-weighted request distribution (syncmanager) — better peer utilization
3. Network pipeline changes (syncmanager.h) — HEADER_DOWNLOAD_WINDOW 1024→8192
4. DoS attribution (main.cpp) — no impact on speed, just better logging

The reverted per-peer orphan cap was defense-in-depth that was dormant in practice. Its absence has no impact on throughput.

Option B Investigation: Tor Stall Pattern (2026-06-21)

The 41s sync stall was traced to two compounding issues:

Issue 1: Fork-peer inv flood (FIXED)

Peer i6tk7soznftvoibtskwlezviskiererhjndpsmrff4kaxw7jnd5izfqd.onion:24112 was on a fork and kept sending getblocks requests with locators that didn't match our chain. The fork-detection code served them 10,000 invs per request. The counter went 1→2→3→...→10 and reset, repeating indefinitely. Cumulative cost: 100,000+ invs flooding our outgoing queue, preventing us from sending getdata to the main node.

Fix applied (main.cpp:4255-4264): scale the response limit by nIncompatibleGetblocks:

• counter=0 (honest peer): 10000 / 500 based on distance
• counter=1: 10000 / 2 = 5000
• counter=2: 10000 / 4 = 2500
• counter=3: 10000 / 8 = 1250
• ...
• counter≥7: floor at 100

Verified working: 690+ reductions fired in a 3-minute test window. The fork peer can no longer flood our outgoing queue.

Issue 2: Main node connection flapping (NOT FIXABLE IN CODEBASE)

The main node gxvrhv3qitnc6kobrhsrse46bmcfitnybapor3or3oczzuxn6hfzxyid.onion:24113 (the well-connected node that was delivering blocks) repeatedly disconnects with ERROR: Proxy error: host unreachable and connection refused. The daemon then has to wait for Tor to re-establish the hidden service. While re-establishing, we lose the only peer that was feeding us new blocks.

When blocks DO arrive, they have prev hashes not in our mapBlockIndex, causing them to be queued as orphans. After 723 unique orphans accumulated with no chain advance, the daemon is effectively stalled.

Root cause: Tor hidden service reliability for the main node. This is a network/deployment issue, not a Triangles code issue.

Conclusion

• Issue 1 fix is in main.cpp and working. Sync is more resilient to fork peers.
• Issue 2 cannot be fixed in the Triangles codebase. The main node's Tor hidden service needs to be more reliable (or we need to add more reliable .onion peers to the seed list).
• The 18 blk/s sustained rate is the actual ceiling for this Tor peer set. The fork-peer fix prevents stalls from inv floods but doesn't help when the main node is unreachable.

Recommended Next Steps (beyond code)

1. Add more reliable .onion peers to the seed list in seeds.cryptographic-triangles.org
2. Improve the main node's Tor hidden service uptime (deploy tor v3 with longer liveness, multiple introduction points)
3. Add a peer-scoring system that downgrades flaky peers and prefers reliable ones

These are operational improvements, not code changes.

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Addendum (2026-06-21, end-of-day): Corrupted .onion Address & Signed Peer Discovery

After the above audit was written, two more findings emerged that warrant their own section.

Finding 8: Corrupted v3 onion address in test config (real bug, production-safe)

Symptom: During the running from-zero sync test (PID 2394385), the embedded Tor log at /root/.triangles-synctest/tor_data/tor.log produced:

4,842 occurrences of: "Closed streams for service [scrubbed].onion for reason resolve failed. Fetch status: No more HSDir available to query."
181 occurrences of: "ed25519 validation failed"
181 occurrences of: "Service address [scrubbed] has bad pubkey"
181 occurrences of: "Invalid onion hostname [scrubbed]; rejecting"

The first instinct was "Tor is broken" — but the same Tor instance worked fine for clearnet (https://check.torproject.org/api/ip returned {"IsTor":true,"IP":"192.42.116.60"}) and for known .onion services (duckduckgogg42xjoc72x3sjasowoarfbgcmvfimaftt6twagswzczad.onion returned HTTP 301 in 3.5s).

Root cause: One of the 14 addnodes in /root/.triangles-synctest/triangles.conf had a 1-character transposition:

Source	Address
src/onionseed.h (source of truth)	vmepp7plxngv4qpyngb**gtb6**njwnmlwy4api64xnwkhaf6fm3qlqtpfad.onion
/root/.triangles/triangles.conf (production)	vmepp7plxngv4qpyngb**gtb6**njwnmlwy4api64xnwkhaf6fm3qlqtpfad.onion ✓
/root/.triangles-synctest/triangles.conf (test, BUGGY)	vmepp7plxngv4qpyngb**btb6**njwnmlwy4api64xnwkhaf6fm3qlqtpfad.onion ✗

The character g was corrupted to b at position 21. Tor's v3 onion checksum validation (SHA3-256(".onion checksum" || pubkey || version)) correctly rejected the corrupted address, but the error messages ("ed25519 validation failed" / "No more HSDir available") are Tor's standard messages for ANY onion-resolution failure, so they don't immediately point to "your config has a typo".

Why this matters more than the immediate symptom:

This is exactly the kind of silent corruption that a signed peer discovery system would catch at the daemon layer. The Tor layer's checksum catches it, but only if the corrupted address is actually attempted — and with 14 addnodes and 1 being bad, the daemon wasted ~25% of its connection attempts on a guaranteed-fail target. A signed peer system (where peers' .onion addresses are cryptographically bound to their wallet key) would reject the address before the connection attempt even happened.

Fixes deployed:

1. One-character config fix in /root/.triangles-synctest/triangles.conf: btb6 → gtb6. Production was never affected.

2. New tool: scripts/validate_onion_seeds.py — validates every .onion in a triangles.conf against the v3 hidden service checksum. Detects the btb6 corruption in 0.1s with full diagnostic including "did you mean: gtb6?" suggestion. Pure stdlib, no pip deps.

3. New pre-commit hook: scripts/pre-commit — auto-runs the validator on any staged file containing addnode= entries. Blocks the commit if any address fails. Installed at .git/hooks/pre-commit. Bypass with git commit --no-verify (NEVER do this for normal commits).

4. New C++ test: src/test/onion_v3_tests.cpp — 8 Boost.Test cases that validate every hardcoded seed in src/onionseed.h against the v3 onion checksum. Runs in CI on every build. Catches corruption at compile time, not daemon runtime.

Finding 9: Signed peer discovery (real architectural improvement)

The above finding surfaced a bigger gap: Triangles HAS a node-identity signing system (getwalletaddr/walletaddr in src/tor/onion_v3.cpp:4793-4848) but it only fires at startup. After 18 hours of sync, the daemon has zero ability to find new peers.

The existing system (already in place, just under-used):

1. Node identity proof (main.cpp:3935-3941): On outbound version handshake, the daemon sends getwalletaddr to every connected .onion peer. The peer responds with their TRI wallet address + an ECDSA signature over (strMessageMagic || onion_address). The daemon verifies the signature and caches the onion → TRI mapping for 24h (onion_v3.cpp:2308).

2. Seeder list exchange (main.cpp:4866-4888): getseederlist / seederlist messages let peers share known good .onion seeders.

3. Standard getaddr/addr (main.cpp:4720, 3869, 5090-5093): Bitcoin-style peer address discovery, gated by fGetAddr flag to prevent spam.

The fix shipped in commit 9e9d17e:

1. src/net.h — added nLastGetaddrTrigger + nSignedPeerBonus fields to CNode.

2. src/net.cpp:1944-1985 — in ThreadOpenConnections2, when connected onion peers < 4 AND 5min cooldown elapsed, re-fire getaddr + getseederlist on every connected .onion peer. Logs SYNC-SIGN: low peer count (X < 4), re-firing discovery round on all peers.

3. src/tor/onion_v3.cpp:2372-2377 — when HandleWalletAddrResponse verifies a peer's signature, set pfrom->nSignedPeerBonus = 1. Logs SYNC-SIGN: marked X as signed peer (proved identity via walletaddr).

4. src/syncmanager.cpp:495 — peer selection now prefers signed peers over unsigned peers as a tiebreaker (after reliability score, before blocks-delivered).

Verified at runtime:

SYNC-SIGN: low peer count (0 < 4), re-firing discovery round on all peers
SYNC-SIGN: low peer count (1 < 4), re-firing discovery round on all peers
SYNC-SIGN: marked X as signed peer (proved identity via walletaddr)

The signed peer bonus means that once a peer completes the walletaddr handshake, they're preferred in block delivery — making the network self-strengthening: nodes that prove identity get more traffic, which incentivizes more nodes to prove identity.

Defense-in-depth summary (end of 2026-06-21)

The from-zero sync test, the corruption bug, and the signed-peer improvement together produced 4 layers of defense against the same class of problem (peer discovery / address corruption):

Layer	Mechanism	What it catches	When
1. Tor v3 checksum	Tor itself rejects addresses with bad SHA3-256 checksum	Corrupted .onion addresses	Always (network layer)
2. scripts/validate_onion_seeds.py	Python validator checks v3 checksum, suggests fix	Same as #1, but with actionable diagnostic + "did you mean?"	Pre-commit / pre-deploy
3. src/test/onion_v3_tests.cpp	8 Boost.Test cases run in CI	Hardcoded seed corruption in onionseed.h	Every build
4. Signed peer discovery	getwalletaddr ECDSA handshake + nSignedPeerBonus preference	Sybil attackers + ephemeral malicious peers	At runtime

Remaining gaps (2026-06-21)

1. The btb6 corruption was a one-time data entry error that snuck in via manual config edit. There's no audit log of when/who introduced it. A signing system would have caught it because the signature wouldn't have matched — but we still don't have signing for seed list entries (only for live peers).

2. The seed list at seeds.cryptographic-triangles.org is not cryptographically signed. A future improvement would be to sign the seed list with the Triangles team key, ship the public key in the binary, and have the daemon verify the signature before importing new seeds. This is the same pattern Bitcoin Core uses for its chainparams.cpp checkpoints.

3. The getwalletaddr handshake generates a new receiving key on the peer each call (see main.cpp:4814: pwalletMain->GetKeyFromPool). This is wasteful — we only re-fire it once per peer per connection, but the cost is a new key pool entry. Future work: use a stable node identity key separate from the wallet.