diff --git a/crates/openshell-cli/src/commands/common.rs b/crates/openshell-cli/src/commands/common.rs
index e6edb4d33..a134ff6f0 100644
--- a/crates/openshell-cli/src/commands/common.rs
+++ b/crates/openshell-cli/src/commands/common.rs
@@ -726,6 +726,11 @@ pub fn parse_duration_to_ms(s: &str) -> Result<i64> {
     let num: i64 = num_str
         .parse()
         .map_err(|_| miette::miette!("invalid duration: {s} (expected e.g. 5m, 1h, 30s)"))?;
+    if num < 0 {
+        return Err(miette::miette!(
+            "duration must not be negative: {s}"
+        ));
+    }
     let multiplier = match unit {
         "s" => 1_000,
         "m" => 60_000,
@@ -736,7 +741,8 @@ pub fn parse_duration_to_ms(s: &str) -> Result<i64> {
             ));
         }
     };
-    Ok(num * multiplier)
+    num.checked_mul(multiplier)
+        .ok_or_else(|| miette::miette!("duration value is too large: {s}"))
 }
 
 // ---------------------------------------------------------------------------
@@ -975,4 +981,24 @@ mod tests {
         let err = parse_duration_to_ms("\u{20ac}").expect_err("missing number should error");
         assert!(err.to_string().contains("invalid duration"));
     }
+
+    #[test]
+    fn parse_duration_to_ms_rejects_overflow() {
+        let err = parse_duration_to_ms("100000000000000h").expect_err("overflow should error");
+        assert!(err.to_string().contains("too large"));
+    }
+
+    #[test]
+    fn parse_duration_to_ms_rejects_negative() {
+        let err = parse_duration_to_ms("-5m").expect_err("negative duration should error");
+        assert!(err.to_string().contains("negative"));
+    }
+
+    #[test]
+    fn parse_duration_to_ms_accepts_zero_and_valid() {
+        assert_eq!(parse_duration_to_ms("0s").unwrap(), 0);
+        assert_eq!(parse_duration_to_ms("30s").unwrap(), 30_000);
+        assert_eq!(parse_duration_to_ms("5m").unwrap(), 300_000);
+        assert_eq!(parse_duration_to_ms("2h").unwrap(), 7_200_000);
+    }
 }
diff --git a/crates/openshell-cli/src/run.rs b/crates/openshell-cli/src/run.rs
index 4843475e5..8622735bd 100644
--- a/crates/openshell-cli/src/run.rs
+++ b/crates/openshell-cli/src/run.rs
@@ -6508,7 +6508,10 @@ pub async fn sandbox_logs(
                 .as_millis(),
         )
         .into_diagnostic()?;
-        now_ms - dur_ms
+        // Negative durations are rejected by parse_duration_to_ms. Overlong
+        // durations are clamped to zero (show all logs since the epoch) rather
+        // than silently producing a future timestamp.
+        now_ms.checked_sub(dur_ms).unwrap_or(0).max(0)
     } else {
         0
     };
diff --git a/crates/openshell-driver-docker/src/lib.rs b/crates/openshell-driver-docker/src/lib.rs
index a196ba6ad..60b04ea2c 100644
--- a/crates/openshell-driver-docker/src/lib.rs
+++ b/crates/openshell-driver-docker/src/lib.rs
@@ -2738,7 +2738,14 @@ fn parse_cpu_limit(value: &str) -> Result<Option<i64>, Status> {
                 "docker cpu_limit must be greater than zero",
             ));
         }
-        return Ok(Some(millicores.saturating_mul(1_000_000)));
+        return millicores
+            .checked_mul(1_000_000)
+            .map(Some)
+            .ok_or_else(|| {
+                Status::failed_precondition(format!(
+                    "docker cpu_limit '{value}' is too large",
+                ))
+            });
     }
 
     let cores = value.parse::<f64>().map_err(|_| {
@@ -2752,7 +2759,15 @@ fn parse_cpu_limit(value: &str) -> Result<Option<i64>, Status> {
         ));
     }
 
-    Ok(Some((cores * 1_000_000_000.0).round() as i64))
+    let nano_cpus = (cores * 1_000_000_000.0).round();
+    #[allow(clippy::cast_precision_loss)]
+    if !nano_cpus.is_finite() || nano_cpus < i64::MIN as f64 || nano_cpus >= i64::MAX as f64 {
+        return Err(Status::failed_precondition(format!(
+            "docker cpu_limit '{value}' is too large",
+        )));
+    }
+
+    Ok(Some(nano_cpus as i64))
 }
 
 #[allow(clippy::cast_possible_truncation)]
@@ -2798,7 +2813,15 @@ fn parse_memory_limit(value: &str) -> Result<Option<i64>, Status> {
         }
     };
 
-    Ok(Some((amount * multiplier).round() as i64))
+    let bytes = (amount * multiplier).round();
+    #[allow(clippy::cast_precision_loss)]
+    if !bytes.is_finite() || bytes < i64::MIN as f64 || bytes >= i64::MAX as f64 {
+        return Err(Status::failed_precondition(format!(
+            "docker memory_limit '{value}' is too large",
+        )));
+    }
+
+    Ok(Some(bytes as i64))
 }
 
 fn sandbox_from_container_summary(summary: &ContainerSummary) -> Option<DriverSandbox> {
diff --git a/crates/openshell-driver-docker/src/tests.rs b/crates/openshell-driver-docker/src/tests.rs
index a86a9936f..0e752d92d 100644
--- a/crates/openshell-driver-docker/src/tests.rs
+++ b/crates/openshell-driver-docker/src/tests.rs
@@ -2250,3 +2250,59 @@ fn container_state_needs_resume_matches_startable_states() {
         );
     }
 }
+
+#[test]
+fn parse_cpu_limit_rejects_overflow() {
+    let err = parse_cpu_limit("1e300").unwrap_err();
+    assert!(err.message().contains("too large"));
+}
+
+#[test]
+fn parse_memory_limit_rejects_overflow() {
+    // 308 nines is finite as f64 (~1e308), but multiplying by Gi overflows to inf.
+    let huge = "9".repeat(308) + "Gi";
+    let err = parse_memory_limit(&huge).unwrap_err();
+    assert!(err.message().contains("too large"));
+}
+
+#[test]
+fn parse_cpu_limit_rejects_i64_max_boundary() {
+    // 9_223_372_036.854776 cores * 1e9 rounds exactly to 2^63, which used to
+    // pass the > check and silently saturate to i64::MAX. It must now be
+    // rejected. (9_223_372_037 is already above the boundary and would also
+    // pass a > guard, so it does not test the equality case.)
+    let err = parse_cpu_limit("9223372036.854776").unwrap_err();
+    assert!(err.message().contains("too large"));
+
+    // One core below the boundary is still valid.
+    assert_eq!(
+        parse_cpu_limit("9223372036").unwrap(),
+        Some(9_223_372_036_000_000_000)
+    );
+}
+
+#[test]
+fn parse_cpu_limit_rejects_millicore_overflow() {
+    // 9_223_372_036_854 millicores * 1_000_000 == 9_223_372_036_854_000_000,
+    // which fits in i64. One millicore more overflows and must be rejected.
+    assert_eq!(
+        parse_cpu_limit("9223372036854m").unwrap(),
+        Some(9_223_372_036_854_000_000)
+    );
+    let err = parse_cpu_limit("9223372036855m").unwrap_err();
+    assert!(err.message().contains("too large"));
+}
+
+#[test]
+fn parse_memory_limit_rejects_i64_max_boundary() {
+    // 8192 PiB = 2^63 bytes, which used to pass the > check and silently
+    // saturate to i64::MAX. It must now be rejected.
+    let err = parse_memory_limit("8192Pi").unwrap_err();
+    assert!(err.message().contains("too large"));
+
+    // One PiB below the boundary is still valid.
+    assert_eq!(
+        parse_memory_limit("8191Pi").unwrap(),
+        Some(8191 * 1024_i64.pow(5))
+    );
+}
diff --git a/crates/openshell-driver-podman/src/container.rs b/crates/openshell-driver-podman/src/container.rs
index 90ef0fec2..eceaa3177 100644
--- a/crates/openshell-driver-podman/src/container.rs
+++ b/crates/openshell-driver-podman/src/container.rs
@@ -1074,7 +1074,25 @@ pub fn build_container_spec_for_image(
                     openshell_core::config::DEFAULT_SSH_PORT
                 ),
             ],
-            interval: config.health_check_interval_secs * 1_000_000_000,
+            interval: {
+                const NS_PER_S: u64 = 1_000_000_000;
+                let max_secs = (i64::MAX as u64) / NS_PER_S;
+                if config.health_check_interval_secs > max_secs {
+                    return Err(ComputeDriverError::InvalidArgument(format!(
+                        "health_check_interval_secs {} exceeds maximum allowed nanoseconds",
+                        config.health_check_interval_secs
+                    )));
+                }
+                config
+                    .health_check_interval_secs
+                    .checked_mul(NS_PER_S)
+                    .ok_or_else(|| {
+                        ComputeDriverError::InvalidArgument(format!(
+                            "health_check_interval_secs {} exceeds maximum allowed nanoseconds",
+                            config.health_check_interval_secs
+                        ))
+                    })?
+            },
             timeout: 2_000_000_000,
             retries: 10,
             start_period: 5_000_000_000,
@@ -1211,8 +1229,13 @@ fn parse_cpu_to_microseconds(quantity: &str) -> Option<u64> {
         if cores <= 0.0 || cores.is_nan() || cores.is_infinite() {
             return None;
         }
+        let micros_f = cores * 100_000.0;
+        #[allow(clippy::cast_precision_loss)]
+        if !micros_f.is_finite() || micros_f >= u64::MAX as f64 {
+            return None;
+        }
         #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
-        let val = (cores * 100_000.0) as u64;
+        let val = micros_f as u64;
         val
     };
     // A quota of 0 microseconds is invalid — treat as no limit.
@@ -1287,6 +1310,56 @@ mod tests {
         assert_eq!(parse_cpu_to_microseconds("0.5"), Some(50_000));
     }
 
+    #[test]
+    fn parse_cpu_huge_value_returns_none_instead_of_overflow() {
+        // A finite f64 whose product with 100_000 overflows to infinity.
+        assert_eq!(parse_cpu_to_microseconds("1e300"), None);
+    }
+
+    #[test]
+    fn parse_cpu_rejects_u64_max_boundary() {
+        // 184_467_440_737_095.51616 cores * 100_000 rounds exactly to 2^64,
+        // which used to pass the > check and silently saturate to u64::MAX.
+        // It must now be rejected. The previous value (184467440737095520)
+        // was ~1000x larger and did not exercise the equality boundary.
+        assert_eq!(parse_cpu_to_microseconds("184467440737095.51616"), None);
+
+        // Just below the boundary is still valid.
+        assert_eq!(
+            parse_cpu_to_microseconds("184467440737095"),
+            Some(18_446_744_073_709_500_416)
+        );
+    }
+
+    #[test]
+    fn container_spec_rejects_health_check_interval_overflow() {
+        let sandbox = test_sandbox("test-id", "test-name");
+        let mut config = test_config();
+        // i64::MAX nanoseconds / 1_000_000_000 ns/s = 9_223_372_036 seconds.
+        // One second over must be rejected before it can saturate.
+        config.health_check_interval_secs = 9_223_372_037;
+        let err = try_build_container_spec_with_token(&sandbox, &config, None).unwrap_err();
+        assert!(
+            matches!(err, ComputeDriverError::InvalidArgument(_)),
+            "expected InvalidArgument, got {err:?}"
+        );
+        assert!(format!("{err}").contains("health_check_interval_secs"));
+    }
+
+    #[test]
+    fn container_spec_accepts_health_check_interval_at_boundary() {
+        let sandbox = test_sandbox("test-id", "test-name");
+        let mut config = test_config();
+        // i64::MAX nanoseconds / 1_000_000_000 ns/s = 9_223_372_036 seconds.
+        const NS_PER_S: u64 = 1_000_000_000;
+        config.health_check_interval_secs = (i64::MAX as u64) / NS_PER_S;
+        let spec = try_build_container_spec_with_token(&sandbox, &config, None).unwrap();
+        let interval = spec["healthconfig"]["Interval"]
+            .as_u64()
+            .expect("healthcheck interval should be a u64");
+        assert_eq!(interval, config.health_check_interval_secs * NS_PER_S);
+    }
+
     #[test]
     fn parse_memory_binary_suffixes() {
         assert_eq!(parse_memory_to_bytes("256Mi"), Some(256 * 1024 * 1024));
diff --git a/crates/openshell-server/src/grpc/sandbox.rs b/crates/openshell-server/src/grpc/sandbox.rs
index 0d6a4e277..06a0362d6 100644
--- a/crates/openshell-server/src/grpc/sandbox.rs
+++ b/crates/openshell-server/src/grpc/sandbox.rs
@@ -1422,7 +1422,14 @@ pub(super) async fn handle_create_ssh_session(
     let token = uuid::Uuid::new_v4().to_string();
     let now_ms = current_time_ms();
     let expires_at_ms = if state.config.ssh_session_ttl_secs > 0 {
-        now_ms + (state.config.ssh_session_ttl_secs as i64 * 1000)
+        let ttl_secs = state.config.ssh_session_ttl_secs;
+        let ttl_ms = i64::try_from(ttl_secs)
+            .map_err(|_| Status::invalid_argument("ssh_session_ttl_secs is too large"))?
+            .checked_mul(1000)
+            .ok_or_else(|| Status::invalid_argument("ssh_session_ttl_secs is too large"))?;
+        now_ms
+            .checked_add(ttl_ms)
+            .ok_or_else(|| Status::invalid_argument("ssh_session_ttl_secs is too large"))?
     } else {
         0
     };
@@ -4016,4 +4023,32 @@ mod tests {
         assert!(session.revoked);
         assert_eq!(session.object_workspace(), "default");
     }
+
+    #[tokio::test]
+    async fn create_ssh_session_rejects_too_large_ttl() {
+        let mut state = test_server_state().await;
+        state
+            .store
+            .put_message(&test_sandbox("ttl-test", Vec::new()))
+            .await
+            .unwrap();
+
+        // Any value larger than i64::MAX seconds cannot be converted to
+        // milliseconds without overflowing.
+        Arc::get_mut(&mut state)
+            .expect("fresh test state is uniquely held")
+            .config
+            .ssh_session_ttl_secs = u64::MAX;
+
+        let err = handle_create_ssh_session(
+            &state,
+            Request::new(CreateSshSessionRequest {
+                sandbox_id: "sandbox-ttl-test".to_string(),
+            }),
+        )
+        .await
+        .unwrap_err();
+        assert_eq!(err.code(), tonic::Code::InvalidArgument);
+        assert!(err.message().contains("ssh_session_ttl_secs is too large"));
+    }
 }
diff --git a/crates/openshell-tui/src/lib.rs b/crates/openshell-tui/src/lib.rs
index b3937e2b9..cd8693178 100644
--- a/crates/openshell-tui/src/lib.rs
+++ b/crates/openshell-tui/src/lib.rs
@@ -2603,11 +2603,10 @@ fn format_age(epoch_ms: i64) -> String {
     let now = std::time::SystemTime::now()
         .duration_since(std::time::UNIX_EPOCH)
         .map_or(0, |d| d.as_secs().cast_signed());
-    let diff = now - created_secs;
-    if diff < 0 {
+    if created_secs > now {
         return String::from("-");
     }
-    let diff = diff.cast_unsigned();
+    let diff = (now - created_secs).cast_unsigned();
     if diff < 60 {
         format!("{diff}s")
     } else if diff < 3600 {
@@ -2649,3 +2648,31 @@ fn days_to_ymd(days: i64) -> (i64, i64, i64) {
     let y = if m <= 2 { y + 1 } else { y };
     (y, m, d)
 }
+
+// ---------------------------------------------------------------------------
+// Tests
+// ---------------------------------------------------------------------------
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn format_age_handles_future_timestamp() {
+        let future_ms = i64::try_from(
+            std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .unwrap()
+                .as_millis(),
+        )
+        .unwrap()
+            + 10_000;
+        assert_eq!(format_age(future_ms), "-");
+    }
+
+    #[test]
+    fn format_age_handles_zero_and_negative() {
+        assert_eq!(format_age(0), "-");
+        assert_eq!(format_age(-1), "-");
+    }
+}