From e026bce50fa2eb687574b4b0bffd0ba4aa3f1072 Mon Sep 17 00:00:00 2001
From: heinrich5991 <heinrich5991@gmail.com>
Date: Tue, 5 Jul 2022 10:17:47 +0200
Subject: [PATCH] Fix out of bounds read in checksum stuff

---
 src/engine/client/client.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/engine/client/client.cpp b/src/engine/client/client.cpp
index 3fbd13151..b3207a590 100644
--- a/src/engine/client/client.cpp
+++ b/src/engine/client/client.cpp
@@ -4131,7 +4131,10 @@ int CClient::HandleChecksum(int Conn, CUuid Uuid, CUnpacker *pUnpacker)
 	sha256_update(&Sha256Ctxt, &Uuid, sizeof(Uuid));
 	sha256_update(&Sha256Ctxt, aStartBytes, sizeof(aStartBytes));
 	sha256_update(&Sha256Ctxt, aEndBytes, sizeof(aEndBytes));
-	sha256_update(&Sha256Ctxt, m_Checksum.m_aBytes + Start, ChecksumBytesEnd - Start);
+	if(Start < (int)sizeof(m_Checksum.m_aBytes))
+	{
+		sha256_update(&Sha256Ctxt, m_Checksum.m_aBytes + Start, ChecksumBytesEnd - Start);
+	}
 	if(End > (int)sizeof(m_Checksum.m_aBytes))
 	{
 		unsigned char aBuf[2048];