util: Don't allow base58-decoding of std::string:s containing non-base58 characters

src/base58.cpp

@@ -7,6 +7,7 @@
 #include <hash.h>
 #include <uint256.h>
 #include <util/strencodings.h>
+#include <util/string.h>
 
 #include <assert.h>
 #include <string.h>
@@ -130,6 +131,9 @@ std::string EncodeBase58(const std::vector<unsigned char>& vch)
 
 bool DecodeBase58(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret_len)
 {
+    if (!ValidAsCString(str)) {
+        return false;
+    }
     return DecodeBase58(str.c_str(), vchRet, max_ret_len);
 }
 
@@ -161,5 +165,8 @@ bool DecodeBase58Check(const char* psz, std::vector<unsigned char>& vchRet, int
 
 bool DecodeBase58Check(const std::string& str, std::vector<unsigned char>& vchRet, int max_ret)
 {
+    if (!ValidAsCString(str)) {
+        return false;
+    }
     return DecodeBase58Check(str.c_str(), vchRet, max_ret);
 }