p2p: restore safe sync mode when target height drops
What the developer wrote
Authored by selsta
p2p: restore safe sync mode when target height drops
What changed, and why it matters
This small patch changes Monero's peer-to-peer sync logic so that when the node's estimated target blockchain height suddenly drops, it re-enables 'safe sync mode' if the target is now very close to the node's current height. Safe sync mode is a more conservative way of downloading and verifying blocks. The change is defensive: without it, a node might stay in a faster but less safe sync mode even when the network no longer appears to be far ahead, which could make it more vulnerable to a malicious peer manipulating its view of the chain height. The commit message does not call this a security fix, and no independent researcher is credited.
Treat as a routine defensive fix. Users running monerod should upgrade to a version containing this commit, especially if they operate nodes exposed to untrusted peers. No urgent mitigation is indicated by the commit itself.
Security signals we found
Defensive hardening against peer height manipulation
Re-enables conservative verification near chain tip
No explicit security framing by vendor
No CVE or advisory referenced in commit
Evidence from the diff
In cryptonote_protocol_handler.inl, when the target height decreases (previous_target > target), the code now calls m_core.safesyncmode(true) if target < current_height + 5. Safe sync mode typically disables some optimizations (like skipping hash checks for blocks assumed to be on the main chain) and is normally enabled near the chain tip. The patch ensures the mode is restored if a previously high target height collapses back near the local tip, preventing the node from remaining in an unsafe fast-sync posture based on stale or inflated peer height data.
Changed components
src/cryptonote_protocol/cryptonote_protocol_handler.inlMonero daemon P2P sync logicsafe sync mode state managementInspect captured patch +2 / −0
diff --git a/src/cryptonote_protocol/cryptonote_protocol_handler.inl b/src/cryptonote_protocol/cryptonote_protocol_handler.inl
index a115d50..071625c 100644
--- a/src/cryptonote_protocol/cryptonote_protocol_handler.inl
+++ b/src/cryptonote_protocol/cryptonote_protocol_handler.inl
@@ -2873,6 +2873,8 @@ skip:
{
MINFO("Target height decreasing from " << previous_target << " to " << target);
m_core.set_target_blockchain_height(target);
+ if (target < m_core.get_current_blockchain_height() + 5)
+ m_core.safesyncmode(true);
if (target == 0 && context.m_state > cryptonote_connection_context::state_before_handshake && !m_stopping)
{
MCWARNING("global", "monerod is now disconnected from the network");
Why this scored 46/100
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