From 2aaf22b0de04f0e472ce8a2e8c4daf0a8d207b5d Mon Sep 17 00:00:00 2001
From: Derek Collison <derek@nats.io>
Date: Wed, 14 Sep 2022 16:47:35 -0700
Subject: [PATCH] For ackMsg, make sure sequence is still relevant as well.

Signed-off-by: Derek Collison <derek@nats.io>
---
 server/stream.go | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/server/stream.go b/server/stream.go
index 89cb7cfd..8800b20f 100644
--- a/server/stream.go
+++ b/server/stream.go
@@ -4582,11 +4582,19 @@ func (mset *stream) checkInterest(seq uint64, obs *consumer) bool {
 
 // ackMsg is called into from a consumer when we have a WorkQueue or Interest Retention Policy.
 func (mset *stream) ackMsg(o *consumer, seq uint64) {
-	var shouldRemove bool
-
-	switch mset.cfg.Retention {
-	case LimitsPolicy:
+	if mset.cfg.Retention == LimitsPolicy {
 		return
+	}
+
+	// Make sure this sequence is not below our first sequence.
+	var state StreamState
+	mset.store.FastState(&state)
+	if seq < state.FirstSeq {
+		return
+	}
+
+	var shouldRemove bool
+	switch mset.cfg.Retention {
 	case WorkQueuePolicy:
 		// Normally we just remove a message when its ack'd here but if we have direct consumers
 		// from sources and/or mirrors we need to make sure they have delivered the msg.