From c56d2c1bbe9e9cada98128a30f777b685d5bdb3e Mon Sep 17 00:00:00 2001
From: atlimit8 <atlimit8-vcs@gmx.com>
Date: Wed, 18 May 2022 23:08:30 -0500
Subject: [PATCH] fix possible underflow in BlowfishKeyProvider.LenBigNum()

---
 OpenRA.Mods.Cnc/FileFormats/BlowfishKeyProvider.cs | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/OpenRA.Mods.Cnc/FileFormats/BlowfishKeyProvider.cs b/OpenRA.Mods.Cnc/FileFormats/BlowfishKeyProvider.cs
index d4ef9f3116..fe93870613 100644
--- a/OpenRA.Mods.Cnc/FileFormats/BlowfishKeyProvider.cs
+++ b/OpenRA.Mods.Cnc/FileFormats/BlowfishKeyProvider.cs
@@ -90,8 +90,14 @@ namespace OpenRA.Mods.Cnc.FileFormats
 
 		static uint LenBigNum(uint[] n, uint len)
 		{
-			var i = len - 1;
-			while (n[i] == 0) i--;
+			if (len == 0)
+				return 0;
+
+			var i = len;
+			while (n[--i] == 0)
+				if (i == 0)
+					return 0; // all zero
+
 			return i + 1;
 		}