diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index a8207a4..d53fa1a 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -2,3 +2,8 @@
 **Vulnerability:** Unvalidated inputs passed to `if()` statements can cause process crashes (`condition has length > 1`) or unexpected coercion vulnerabilities.
 **Learning:** In R, optional boolean parameters that default to `NULL` should be validated using explicit runtime type validation (e.g., `if (!is.null(flag) && (!is.logical(flag) || length(flag) != 1 || is.na(flag)))`).
 **Prevention:** Always implement explicit runtime type validation for optional boolean parameters.
+
+## 2024-07-13 - [Strict Input Validation on Interactive Prompts]
+**Vulnerability:** Unhandled coercion NA exception due to weak integer input validation (`^[0-9]+$`). If a user inputs a massive string (e.g., `"99999999999"`) into `readline()`, `as.integer()` coerces it to `NA`, which then crashes the `if` checks, causing a Denial of Service.
+**Learning:** R does not inherently limit input string length in `readline()` nor does `as.integer()` catch out-of-bound overflow gracefully without introducing an `NA`. Checking for merely `[0-9]+` allows oversized integers.
+**Prevention:** Use strictly bounded exact-match regex like `^[12]$` when reading constrained inputs to ensure coercion functions like `as.integer()` never encounter out-of-bound, `NA`-producing values.
diff --git a/R/aFIPC.R b/R/aFIPC.R
index 6254651..9e11b77 100644
--- a/R/aFIPC.R
+++ b/R/aFIPC.R
@@ -141,7 +141,8 @@ autoFIPC <-
       }
       for (attempt in seq_len(3)) {
         n <- readline(prompt = "Is it correct? (1: Yes 2: No) : ")
-        if (grepl("^[0-9]+$", n)) {
+        # Security: Strict input validation to prevent coercion crashes
+        if (grepl("^[12]$", n)) {
           return(as.integer(n))
         }
       }
@@ -171,7 +172,8 @@ autoFIPC <-
               readline(
                 prompt = "Do you want to use default BILOG-MG priors for oldform Data? (1: Yes 2: No) : "
               )
-            if (grepl("^[0-9]+$", n)) {
+            # Security: Strict input validation to prevent coercion crashes
+            if (grepl("^[12]$", n)) {
               return(as.integer(n))
             }
           }
@@ -390,7 +392,8 @@ autoFIPC <-
               readline(
                 prompt = "Do you want to use default BILOG-MG priors for newform Data? (1: Yes 2: No) : "
               )
-            if (grepl("^[0-9]+$", n)) {
+            # Security: Strict input validation to prevent coercion crashes
+            if (grepl("^[12]$", n)) {
               return(as.integer(n))
             }
           }
diff --git a/tests/testthat/test-sentinel-validation.R b/tests/testthat/test-sentinel-validation.R
index 900f0ee..74876d5 100644
--- a/tests/testthat/test-sentinel-validation.R
+++ b/tests/testthat/test-sentinel-validation.R
@@ -1,3 +1,5 @@
+library(mockery)
+
 test_that("autoFIPC validates boolean flags for newformBILOGprior, oldformBILOGprior, and confirmCommonItems", {
   # newformBILOGprior
   expect_error(
@@ -35,3 +37,22 @@ test_that("autoFIPC validates boolean flags for newformBILOGprior, oldformBILOGp
     "Security Error: confirmCommonItems must be a single non-NA logical value or NULL"
   )
 })
+
+test_that("autoFIPC validates interactive common item correctly with mocks", {
+  # Mock interactive to TRUE to test the readline loops
+  mockery::stub(aFIPC::autoFIPC, 'interactive', TRUE)
+
+  # Stub readline to return an invalid option '3' 3 times, which should exhaust attempts
+  mockery::stub(aFIPC::autoFIPC, 'readline', mockery::mock('3', '3', '3'))
+
+  expect_error(
+    aFIPC::autoFIPC(
+      newformXData = data.frame(A=1),
+      oldformYData = data.frame(A=2),
+      newformCommonItemNames = c('A'),
+      oldformCommonItemNames = c('A'),
+      confirmCommonItems = NULL
+    ),
+    "Too many invalid common item confirmation attempts"
+  )
+})