diff --git a/client/client_state.h b/client/client_state.h
index c1bbb2b9e91..b43131cb010 100644
--- a/client/client_state.h
+++ b/client/client_state.h
@@ -1,6 +1,6 @@
 // This file is part of BOINC.
 // http://boinc.berkeley.edu
-// Copyright (C) 2022 University of California
+// Copyright (C) 2023 University of California
 //
 // BOINC is free software; you can redistribute it and/or modify it
 // under the terms of the GNU Lesser General Public License
@@ -128,7 +128,7 @@ struct CLIENT_STATE {
         // - (Mac) client was started from screensaver,
         //   which has since exited
     bool os_requested_suspend;
-        // we should suspend for OS reasonts (used on Win only).
+        // we should suspend for OS reasons (used on Win only).
         // Set when
         // - got BATTERY_LOW, SUSPEND, SERVICE_CONTROL_PAUSE
     double os_requested_suspend_time;
@@ -431,6 +431,7 @@ struct CLIENT_STATE {
         const char* fname = GLOBAL_PREFS_FILE_NAME,
         const char* override_fname = GLOBAL_PREFS_OVERRIDE_FILE
     );
+    void validate_global_prefs(const GLOBAL_PREFS_MASK& mask);
     void print_global_prefs();
     int save_global_prefs(const char* prefs, char* url, char* sched);
     double available_ram();
diff --git a/client/cs_prefs.cpp b/client/cs_prefs.cpp
index d73e497aa69..be9363a5c07 100644
--- a/client/cs_prefs.cpp
+++ b/client/cs_prefs.cpp
@@ -661,6 +661,7 @@ void CLIENT_STATE::read_global_prefs(
             msg_printf(NULL, MSG_INFO, "Reading preferences override file");
             fclose(f);
             global_prefs.override_file_present = true;
+            validate_global_prefs(mask);
         }
     }
 
@@ -684,6 +685,279 @@ void CLIENT_STATE::read_global_prefs(
 #endif
 }
 
+// Validates preferences that were parsed.  Uses the mask structure, so
+// this should be called immediately after parsing.  This function will check if
+// any preferences are out of a reasonable range for each variable.  This could be
+// any of the following:
+// 1. A negative number.
+// 2. Maximum limits.
+// 3. Checking to make sure a percentage is between 0% and 100%.
+// 4. A time variable that is out of range.
+// If the variable is out of range, it will either be set to the default value, 0,
+// 0%, 100%, 0:00, or 24:00, depending on the variable.  Default values are derived
+// from GLOBAL_PREFS::defaults().
+// Any new preference variables added should be validated here as well.
+//
+void CLIENT_STATE::validate_global_prefs(const GLOBAL_PREFS_MASK& mask) {
+    // ubound is an upper limit for doubles as a sanity check.  This matches
+    // the upper limit as preferences are validated from the Manager.  Refer to
+    // CDlgAdvPreferences::ValidateInput as an example.
+    //
+    double const ubound = 9999999999999.99;
+    char* outrange = "is out of range. Setting changed to";
+    char* timechange = "is not a valid time. Setting changed to";
+    char* forday = "for day";
+    if (mask.battery_charge_min_pct) {
+        if (global_prefs.battery_charge_min_pct < 0) {
+            global_prefs.battery_charge_min_pct = 90;
+            msg_printf(0, MSG_USER_ALERT, "'battery_charge_min_pct' %s 90.", outrange);
+        } else if (global_prefs.battery_charge_min_pct > 100) {
+            global_prefs.battery_charge_min_pct = 100;
+            msg_printf(0, MSG_USER_ALERT, "'battery_charge_min_pct' %s 100.", outrange);
+        }
+    }
+    if (mask.battery_max_temperature) {
+        if (global_prefs.battery_max_temperature < -273.15 || global_prefs.battery_max_temperature > ubound) {
+            global_prefs.battery_max_temperature = 40;
+            msg_printf(0, MSG_USER_ALERT, "'battery_max_temperature' %s 40.", outrange);
+        }
+    }
+    if (mask.idle_time_to_run) {
+        if (global_prefs.idle_time_to_run < 0 || global_prefs.idle_time_to_run > ubound) {
+            global_prefs.idle_time_to_run = 3;
+            msg_printf(0, MSG_USER_ALERT, "'idle_time_to_run' %s 3.", outrange);
+        }
+    }
+    if (mask.suspend_if_no_recent_input) {
+        if (global_prefs.suspend_if_no_recent_input < 0 || global_prefs.suspend_if_no_recent_input > ubound) {
+            global_prefs.suspend_if_no_recent_input = 0;
+            msg_printf(0, MSG_USER_ALERT, "'suspend_if_no_recent_input' %s 0.", outrange);
+        }
+    }
+    if (mask.suspend_cpu_usage) {
+        if (global_prefs.suspend_cpu_usage < 0) {
+            global_prefs.suspend_cpu_usage = 25;
+            msg_printf(0, MSG_USER_ALERT, "'suspend_cpu_usage' %s 25.", outrange);
+        } else if (global_prefs.suspend_cpu_usage > 100) {
+            global_prefs.suspend_cpu_usage = 100;
+            msg_printf(0, MSG_USER_ALERT, "'suspend_cpu_usage' %s 100.", outrange);
+        }
+    }
+    if (mask.niu_suspend_cpu_usage) {
+        if (global_prefs.niu_suspend_cpu_usage < 0) {
+            global_prefs.niu_suspend_cpu_usage = 50;
+            msg_printf(0, MSG_USER_ALERT, "'niu_suspend_cpu_usage' %s 50.", outrange);
+        } else if (global_prefs.niu_suspend_cpu_usage > 100) {
+            global_prefs.niu_suspend_cpu_usage = 100;
+            msg_printf(0, MSG_USER_ALERT, "'niu_suspend_cpu_usage' %s 100.", outrange);
+        }
+    }
+    if (mask.start_hour) {
+        if (global_prefs.cpu_times.start_hour < 0) {
+            global_prefs.cpu_times.start_hour = 0;
+            msg_printf(0, MSG_USER_ALERT, "'start_hour' %s 0:00.", timechange);
+        } else if (global_prefs.cpu_times.start_hour > 24) {
+            global_prefs.cpu_times.start_hour = 24;
+            msg_printf(0, MSG_USER_ALERT, "'start_hour' %s 24:00.", timechange);
+        }
+    }
+    if (mask.end_hour) {
+        if (global_prefs.cpu_times.end_hour < 0) {
+            global_prefs.cpu_times.end_hour = 0;
+            msg_printf(0, MSG_USER_ALERT, "'end_hour' %s 0:00.", timechange);
+        } else if (global_prefs.cpu_times.end_hour > 24) {
+            global_prefs.cpu_times.end_hour = 24;
+            msg_printf(0, MSG_USER_ALERT, "'end_hour' %s 24:00.", timechange);
+        }
+    }
+    if (mask.net_start_hour) {
+        if (global_prefs.net_times.start_hour < 0) {
+            global_prefs.net_times.start_hour = 0;
+            msg_printf(0, MSG_USER_ALERT, "'net_start_hour' %s 0:00.", timechange);
+        } else if (global_prefs.net_times.start_hour > 24) {
+            global_prefs.net_times.start_hour = 24;
+            msg_printf(0, MSG_USER_ALERT, "'net_start_hour' %s 24:00.", timechange);
+        }
+    }
+    if (mask.net_end_hour) {
+        if (global_prefs.net_times.end_hour < 0) {
+            global_prefs.net_times.end_hour = 0;
+            msg_printf(0, MSG_USER_ALERT, "'net_end_hour' %s 0:00.", timechange);
+        } else if (global_prefs.net_times.end_hour > 24) {
+            global_prefs.net_times.end_hour = 24;
+            msg_printf(0, MSG_USER_ALERT, "'net_end_hour' %s 24:00.", timechange);
+        }
+    }
+    // Validate day-of-week override preferences, if set.
+    for (int i = 0; i < 7; i++) {
+        if (global_prefs.cpu_times.week.days[i].present) {
+            if (global_prefs.cpu_times.week.days[i].start_hour < 0) {
+                global_prefs.cpu_times.week.days[i].start_hour = 0;
+                msg_printf(0, MSG_USER_ALERT, "'start_hour' %s %d %s 0:00", forday, i, timechange);
+            } else if (global_prefs.cpu_times.week.days[i].start_hour > 24) {
+                global_prefs.cpu_times.week.days[i].start_hour = 24;
+                msg_printf(0, MSG_USER_ALERT, "'start_hour' %s %d %s 24:00", forday, i, timechange);
+            }
+            if (global_prefs.cpu_times.week.days[i].end_hour < 0) {
+                global_prefs.cpu_times.week.days[i].end_hour = 0;
+                msg_printf(0, MSG_USER_ALERT, "'end_hour' %s %d %s 0:00", forday, i, timechange);
+            } else if (global_prefs.cpu_times.week.days[i].end_hour > 24) {
+                global_prefs.cpu_times.week.days[i].end_hour = 24;
+                msg_printf(0, MSG_USER_ALERT, "'end_hour' %s %d %s 24:00", forday, i, timechange);
+            }
+        }
+        if (global_prefs.net_times.week.days[i].present) {
+            if (global_prefs.net_times.week.days[i].start_hour < 0) {
+                global_prefs.net_times.week.days[i].start_hour = 0;
+                msg_printf(0, MSG_USER_ALERT, "'net_start_hour' %s %d %s 0:00", forday, i, timechange);
+            } else if (global_prefs.net_times.week.days[i].start_hour > 24) {
+                global_prefs.net_times.week.days[i].start_hour = 24;
+                msg_printf(0, MSG_USER_ALERT, "'net_start_hour' %s %d %s 24:00", forday, i, timechange);
+            }
+            if (global_prefs.net_times.week.days[i].end_hour < 0) {
+                global_prefs.net_times.week.days[i].end_hour = 0;
+                msg_printf(0, MSG_USER_ALERT, "'net_end_hour' %s %d %s 00:00", forday, i, timechange);
+            } else if (global_prefs.net_times.week.days[i].end_hour > 24) {
+                global_prefs.net_times.week.days[i].end_hour = 24;
+                msg_printf(0, MSG_USER_ALERT, "'net_end_hour' %s %d %s 24:00", forday, i, timechange);
+            }
+        }
+    }
+    if (mask.work_buf_min_days) {
+        if (global_prefs.work_buf_min_days < 0 || global_prefs.work_buf_min_days > 10) {
+            global_prefs.work_buf_min_days = 0.1;
+            msg_printf(0, MSG_USER_ALERT, "'work_buf_min_days' %s 0.1.", outrange);
+        }
+    }
+    if (mask.work_buf_additional_days) {
+        if (global_prefs.work_buf_additional_days < 0 || global_prefs.work_buf_additional_days > 10) {
+            global_prefs.work_buf_additional_days = 0.5;
+            msg_printf(0, MSG_USER_ALERT, "'work_buf_additional_days' %s 0.5.", outrange);
+        }
+    }
+    if (mask.max_ncpus_pct) {
+        if (global_prefs.max_ncpus_pct < 0) {
+#ifdef ANDROID
+            global_prefs.max_ncpus_pct = 50;
+            msg_printf(0, MSG_USER_ALERT, "'max_ncpus_pct' %s 50.", outrange);
+#else
+            global_prefs.max_ncpus_pct = 0;
+            msg_printf(0, MSG_USER_ALERT, "'max_ncpus_pct' %s 0.", outrange);
+#endif
+        } else if (global_prefs.max_ncpus_pct > 100) {
+            global_prefs.max_ncpus_pct = 100;
+            msg_printf(0, MSG_USER_ALERT, "'max_ncpus_pct' %s 100.", outrange);
+        }
+    }
+    if (mask.niu_max_ncpus_pct) {
+        if (global_prefs.niu_max_ncpus_pct < 0) {
+            global_prefs.niu_max_ncpus_pct = 0;
+            msg_printf(0, MSG_USER_ALERT, "'niu_max_ncpus_pct' %s 0.", outrange);
+        } else if (global_prefs.niu_max_ncpus_pct > 100) {
+            global_prefs.niu_max_ncpus_pct = 100;
+            msg_printf(0, MSG_USER_ALERT, "'niu_max_ncpus_pct' %s 100.", outrange);
+        }
+    }
+    if (mask.max_ncpus) {
+        if (global_prefs.max_ncpus < 0 || global_prefs.max_ncpus > ubound) {
+            global_prefs.max_ncpus = 0;
+            msg_printf(0, MSG_USER_ALERT, "'max_ncpus' %s 0.", outrange);
+        }
+    }
+    if (mask.disk_interval) {
+        if (global_prefs.disk_interval < 0 || global_prefs.disk_interval > ubound) {
+            global_prefs.disk_interval = 60;
+            msg_printf(0, MSG_USER_ALERT, "'disk_interval' %s 60.", outrange);
+        }
+    }
+    if (mask.cpu_scheduling_period_minutes) {
+        if (global_prefs.cpu_scheduling_period_minutes < 0.0001 || global_prefs.cpu_scheduling_period_minutes > ubound) {
+            global_prefs.cpu_scheduling_period_minutes = 60;
+            msg_printf(0, MSG_USER_ALERT, "'cpu_scheduling_period_minutes' %s 60.", outrange);
+        }
+    }
+    if (mask.disk_max_used_gb) {
+        if (global_prefs.disk_max_used_gb < 0 || global_prefs.disk_max_used_gb > ubound) {
+            global_prefs.disk_max_used_gb = 0;
+            msg_printf(0, MSG_USER_ALERT, "'disk_max_used_gb' %s 0.", outrange);
+        }
+    }
+    if (mask.disk_max_used_pct) {
+        if (global_prefs.disk_max_used_pct < 0) {
+            global_prefs.disk_max_used_pct = 90;
+            msg_printf(0, MSG_USER_ALERT, "'disk_max_used_pct' %s 90.", outrange);
+        } else if (global_prefs.disk_max_used_pct > 100) {
+            global_prefs.disk_max_used_pct = 100;
+            msg_printf(0, MSG_USER_ALERT, "'disk_max_used_pct' %s 100.", outrange);
+        }
+    }
+    if (mask.disk_min_free_gb) {
+        if (global_prefs.disk_min_free_gb < 0 || global_prefs.disk_min_free_gb > ubound) {
+            global_prefs.disk_min_free_gb = 0.1;
+            msg_printf(0, MSG_USER_ALERT, "'disk_min_free_gb' %s 0.1.", outrange);
+        }
+    }
+    if (mask.vm_max_used_frac) {
+        if (global_prefs.vm_max_used_frac < 0 || global_prefs.vm_max_used_frac > 1) {
+            global_prefs.vm_max_used_frac = 0.75;
+            msg_printf(0, MSG_USER_ALERT, "'vm_max_used_frac' %s 0.75.", outrange);
+        }
+    }
+    if (mask.ram_max_used_busy_frac) {
+        if (global_prefs.ram_max_used_busy_frac < 0 || global_prefs.ram_max_used_busy_frac > 1) {
+            global_prefs.ram_max_used_busy_frac = 0.5;
+            msg_printf(0, MSG_USER_ALERT, "'ram_max_used_busy_frac' %s 0.5.", outrange);
+        }
+    }
+    if (mask.ram_max_used_idle_frac) {
+        if (global_prefs.ram_max_used_idle_frac < 0 || global_prefs.ram_max_used_idle_frac >1) {
+#ifdef ANDROID
+            global_prefs.ram_max_used_idle_frac = 0.5;
+            msg_printf(0, MSG_USER_ALERT, "'ram_max_used_idle_frac' %s 0.5.", outrange);
+#else
+            global_prefs.ram_max_used_idle_frac = 0.9;
+            msg_printf(0, MSG_USER_ALERT, "'ram_max_used_idle_frac' %s 0.9.", outrange);
+#endif
+        }
+    }
+    if (mask.max_bytes_sec_up) {
+        if (global_prefs.max_bytes_sec_up < 0 || global_prefs.max_bytes_sec_up > ubound) {
+            global_prefs.max_bytes_sec_up = 0;
+            msg_printf(0, MSG_USER_ALERT, "'max_bytes_sec_up' %s 0.", outrange);
+        }
+    }
+    if (mask.max_bytes_sec_down) {
+        if (global_prefs.max_bytes_sec_down < 0 || global_prefs.max_bytes_sec_down > ubound) {
+            global_prefs.max_bytes_sec_down = 0;
+            msg_printf(0, MSG_USER_ALERT, "'max_bytes_sec_down' %s 0.", outrange);
+        }
+    }
+    if (mask.cpu_usage_limit) {
+        if (global_prefs.cpu_usage_limit < 0 || global_prefs.cpu_usage_limit > 100) {
+            global_prefs.cpu_usage_limit = 100;
+            msg_printf(0, MSG_USER_ALERT, "'cpu_usage_limit' %s 100.", outrange);
+        }
+    }
+    if (mask.niu_cpu_usage_limit) {
+        if (global_prefs.niu_cpu_usage_limit < 0 || global_prefs.niu_cpu_usage_limit > 100) {
+            global_prefs.niu_cpu_usage_limit = 100;
+            msg_printf(0, MSG_USER_ALERT, "'niu_cpu_usage_limit' %s 100.", outrange);
+        }
+    }
+    if (mask.daily_xfer_limit_mb) {
+        if (global_prefs.daily_xfer_limit_mb < 0 || global_prefs.daily_xfer_limit_mb > ubound) {
+            global_prefs.daily_xfer_limit_mb = 0;
+            msg_printf(0, MSG_USER_ALERT, "'daily_xfer_limit_mb' %s 0.", outrange);
+        }
+    }
+    if (mask.daily_xfer_period_days) {
+        if (global_prefs.daily_xfer_period_days < 0 || global_prefs.daily_xfer_period_days > ubound) {
+            global_prefs.daily_xfer_period_days = 0;
+            msg_printf(0, MSG_USER_ALERT, "'daily_xfer_period_days' %s 0.", outrange);
+        }
+    }
+}
+
 void CLIENT_STATE::print_global_prefs() {
     msg_printf(NULL, MSG_INFO, "Preferences:");
 
diff --git a/lib/prefs.cpp b/lib/prefs.cpp
index 5016cc23e82..19c48cf719c 100644
--- a/lib/prefs.cpp
+++ b/lib/prefs.cpp
@@ -331,6 +331,10 @@ int GLOBAL_PREFS::parse_day(XML_PARSER& xp) {
     while (!xp.get_tag()) {
         if (!xp.is_tag) continue;
         if (xp.match_tag("/day_prefs")) {
+            // The day of the week is validated here because the struct TIME_SPAN
+            // is an array of a fixed size.  For validating the start_hour and
+            // end_hour, refer to CLIENT_STATE::validate_global_prefs in cs_prefs.cpp.
+            //
             if (day_of_week < 0 || day_of_week > 6) return ERR_XML_PARSE;
             if (has_cpu) {
                 cpu_times.week.set(day_of_week, start_hour, end_hour);
@@ -380,7 +384,6 @@ int GLOBAL_PREFS::parse_override(
     char buf2[256], attrs[256];
     bool in_venue = false, in_correct_venue=false;
     double dtemp;
-    int itemp;
 
     found_venue = false;
     mask.clear();
@@ -519,39 +522,30 @@ int GLOBAL_PREFS::parse_override(
             continue;
         }
         if (xp.parse_double("work_buf_min_days", work_buf_min_days)) {
-            if (work_buf_min_days < 0) work_buf_min_days = 0;
             mask.work_buf_min_days = true;
             continue;
         }
         if (xp.parse_double("work_buf_additional_days", work_buf_additional_days)) {
-            if (work_buf_additional_days < 0) work_buf_additional_days = 0;
             mask.work_buf_additional_days = true;
             continue;
         }
         if (xp.parse_double("max_ncpus_pct", max_ncpus_pct)) {
-            if (max_ncpus_pct < 0) max_ncpus_pct = 0;
-            if (max_ncpus_pct > 100) max_ncpus_pct = 100;
             mask.max_ncpus_pct = true;
             continue;
         }
         if (xp.parse_double("niu_max_ncpus_pct", niu_max_ncpus_pct)) {
-            if (niu_max_ncpus_pct <= 0) niu_max_ncpus_pct = 100;
-            if (niu_max_ncpus_pct > 100) niu_max_ncpus_pct = 100;
             mask.niu_max_ncpus_pct = true;
             continue;
         }
         if (xp.parse_int("max_cpus", max_ncpus)) {
-            if (max_ncpus < 0) max_ncpus = 0;
             mask.max_ncpus = true;
             continue;
         }
         if (xp.parse_double("disk_interval", disk_interval)) {
-            if (disk_interval<0) disk_interval = 0;
             mask.disk_interval = true;
             continue;
         }
         if (xp.parse_double("cpu_scheduling_period_minutes", cpu_scheduling_period_minutes)) {
-            if (cpu_scheduling_period_minutes < 0.0001) cpu_scheduling_period_minutes = 60;
             mask.cpu_scheduling_period_minutes = true;
             continue;
         }
@@ -585,41 +579,27 @@ int GLOBAL_PREFS::parse_override(
             continue;
         }
         if (xp.parse_double("max_bytes_sec_up", max_bytes_sec_up)) {
-            if (max_bytes_sec_up < 0) max_bytes_sec_up = 0;
             mask.max_bytes_sec_up = true;
             continue;
         }
         if (xp.parse_double("max_bytes_sec_down", max_bytes_sec_down)) {
-            if (max_bytes_sec_down < 0) max_bytes_sec_down = 0;
             mask.max_bytes_sec_down = true;
             continue;
         }
-        if (xp.parse_double("cpu_usage_limit", dtemp)) {
-            if (dtemp > 0 && dtemp <= 100) {
-                cpu_usage_limit = dtemp;
-                mask.cpu_usage_limit = true;
-            }
+        if (xp.parse_double("cpu_usage_limit", cpu_usage_limit)) {
+            mask.cpu_usage_limit = true;
             continue;
         }
-        if (xp.parse_double("niu_cpu_usage_limit", dtemp)) {
-            if (dtemp <= 0) dtemp = 100;
-            if (dtemp > 100) dtemp = 100;
-            niu_cpu_usage_limit = dtemp;
+        if (xp.parse_double("niu_cpu_usage_limit", niu_cpu_usage_limit)) {
             mask.niu_cpu_usage_limit = true;
             continue;
         }
-        if (xp.parse_double("daily_xfer_limit_mb", dtemp)) {
-            if (dtemp >= 0) {
-                daily_xfer_limit_mb = dtemp;
-                mask.daily_xfer_limit_mb = true;
-            }
+        if (xp.parse_double("daily_xfer_limit_mb", daily_xfer_limit_mb)) {
+            mask.daily_xfer_limit_mb = true;
             continue;
         }
-        if (xp.parse_int("daily_xfer_period_days", itemp)) {
-            if (itemp >= 0) {
-                daily_xfer_period_days = itemp;
-                mask.daily_xfer_period_days = true;
-            }
+        if (xp.parse_int("daily_xfer_period_days", daily_xfer_period_days)) {
+            mask.daily_xfer_period_days = true;
             continue;
         }
         if (xp.parse_bool("network_wifi_only", network_wifi_only)) {