From da3eb82e961486573d65a88c17def486cf92129a Mon Sep 17 00:00:00 2001
From: Kris Nuttycombe <kris@electriccoin.co>
Date: Wed, 31 Mar 2021 16:17:32 -0600
Subject: [PATCH] Ensure that Sapling version range checks are always guarded
 by SAPLING_VERSION_GROUP_ID

---
 src/main.cpp | 31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index a924aff71..8d6d7179d 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -883,14 +883,14 @@ bool ContextualCheckTransaction(
     // Rules that apply to Sapling and later:
     if (saplingActive) {
         // Reject transactions with invalid version
-        if (tx.nVersion < SAPLING_MIN_TX_VERSION) {
-            return state.DoS(
-                dosLevelConstricting,
-                error("ContextualCheckTransaction(): Sapling version too low"),
-                REJECT_INVALID, "bad-tx-sapling-version-too-low");
-        }
+        if (tx.nVersionGroupId == SAPLING_VERSION_GROUP_ID) {
+            if (tx.nVersion < SAPLING_MIN_TX_VERSION) {
+                return state.DoS(
+                    dosLevelConstricting,
+                    error("ContextualCheckTransaction(): Sapling version too low"),
+                    REJECT_INVALID, "bad-tx-sapling-version-too-low");
+            }
 
-        if (!futureActive) {
             // Reject transactions with invalid version
             if (tx.nVersion > SAPLING_MAX_TX_VERSION) {
                 return state.DoS(
@@ -898,7 +898,9 @@ bool ContextualCheckTransaction(
                     error("ContextualCheckTransaction(): Sapling version too high"),
                     REJECT_INVALID, "bad-tx-sapling-version-too-high");
             }
+        }
 
+        if (!futureActive) {
             // Reject transactions with invalid version group id
             if (tx.nVersionGroupId != SAPLING_VERSION_GROUP_ID) {
                 return state.DoS(
@@ -1041,6 +1043,13 @@ bool ContextualCheckTransaction(
     if (futureActive) {
         // version group is the most recent available version group ID
         if (tx.nVersionGroupId == ZFUTURE_VERSION_GROUP_ID) {
+            if (tx.nVersion <= SAPLING_MAX_TX_VERSION) {
+                return state.DoS(
+                    dosLevelConstricting,
+                    error("ContextualCheckTransaction(): Future version too low"),
+                    REJECT_INVALID, "bad-tx-zfuture-version-too-low");
+            }
+
             // Reject transactions with invalid version
             if (tx.nVersion > SAPLING_MAX_TX_VERSION + 1) {
                 return state.DoS(
@@ -1049,13 +1058,7 @@ bool ContextualCheckTransaction(
                     REJECT_INVALID, "bad-tx-zfuture-version-too-high");
             }
         } else if (tx.nVersionGroupId == SAPLING_VERSION_GROUP_ID) {
-            // Reject transactions with invalid version
-            if (tx.nVersion > SAPLING_MAX_TX_VERSION) {
-                return state.DoS(
-                    dosLevelPotentiallyRelaxing,
-                    error("ContextualCheckTransaction(): Sapling version too high"),
-                    REJECT_INVALID, "bad-tx-sapling-version-too-high");
-            }
+            //allow V4 transactions while futureActive
         } else {
             return state.DoS(
                 dosLevelPotentiallyRelaxing,