diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index a8207a48..157188aa 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -2,3 +2,7 @@
 **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.
+## 2024-07-25 - Fix weak regex validation causing integer overflow DoS
+**Vulnerability:** Weak regex `^[0-9]+$` allows arbitrarily large numeric strings that coerce to `NA` when cast to integer, causing crash/DoS when passed to `if()`.
+**Learning:** When reading bounded numeric options via `readline()` in R, avoid weak numeric regex as large inputs will overflow native integer coercion, breaking unhandled boolean contexts.
+**Prevention:** Use strictly bounded exact-match regex like `^[12]$` when validating constrained terminal inputs to prevent unexpected `NA` coercions.
diff --git a/DESCRIPTION b/DESCRIPTION
index f31d3e1a..c90753c5 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -10,7 +10,7 @@ Description: Automates fixed item parameter linking for test linking under
     the item response theory paradigm using mirt package estimates.
 License: GPL-3 | file LICENSE
 Imports: mirt, methods
-Suggests: testthat (>= 3.0.0)
+Suggests: testthat (>= 3.0.0), mockery
 Encoding: UTF-8
 Config/testthat/edition: 3
 Config/roxygen2/version: 8.0.0
diff --git a/R/aFIPC.R b/R/aFIPC.R
index 62546519..918e19b1 100644
--- a/R/aFIPC.R
+++ b/R/aFIPC.R
@@ -141,7 +141,7 @@ autoFIPC <-
       }
       for (attempt in seq_len(3)) {
         n <- readline(prompt = "Is it correct? (1: Yes 2: No) : ")
-        if (grepl("^[0-9]+$", n)) {
+        if (grepl("^[12]$", n)) {
           return(as.integer(n))
         }
       }
@@ -171,7 +171,7 @@ autoFIPC <-
               readline(
                 prompt = "Do you want to use default BILOG-MG priors for oldform Data? (1: Yes 2: No) : "
               )
-            if (grepl("^[0-9]+$", n)) {
+            if (grepl("^[12]$", n)) {
               return(as.integer(n))
             }
           }
@@ -390,7 +390,7 @@ autoFIPC <-
               readline(
                 prompt = "Do you want to use default BILOG-MG priors for newform Data? (1: Yes 2: No) : "
               )
-            if (grepl("^[0-9]+$", n)) {
+            if (grepl("^[12]$", n)) {
               return(as.integer(n))
             }
           }
diff --git a/tests/testthat/test-readline.R b/tests/testthat/test-readline.R
new file mode 100644
index 00000000..720ee514
--- /dev/null
+++ b/tests/testthat/test-readline.R
@@ -0,0 +1,30 @@
+library(testthat)
+
+test_that("autoFIPC handles invalid readline inputs securely", {
+  # We test the actual aFIPC::autoFIPC function using mockery to stub readline
+  # We use mockery::stub on the internal functions that call readline
+
+  # Dummy input data
+  new_model <- data.frame(matrix(rnorm(20), nrow=10))
+  old_model <- data.frame(matrix(rnorm(20), nrow=10))
+
+  # Stub interactive to return TRUE so we enter the readline branch
+  mockery::stub(autoFIPC, 'interactive', TRUE)
+
+  # Mock readline to return a large number that caused the NA DoS previously
+  # We use forced failure to simulate the 3 failed attempts
+  mock_readline <- mockery::mock("1000000000000", "1000000000000", "1000000000000")
+  mockery::stub(autoFIPC, 'readline', mock_readline)
+
+  # When confirmCommonItems is NULL, it prompts. If it fails 3 times, it stops.
+  expect_error(
+    autoFIPC(
+      newformXData = new_model,
+      oldformYData = old_model,
+      newformCommonItemNames = "X1",
+      oldformCommonItemNames = "X1",
+      confirmCommonItems = NULL
+    ),
+    "Too many invalid common item confirmation attempts"
+  )
+})