diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index a8207a4..4065d3d 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 missing input validation in readline prompts
+**Vulnerability:** Weak regex `^[0-9]+$` in interactive `readline()` prompts allowed arbitrarily large numeric strings to be passed. When cast via `as.integer()`, these resulted in `NA`, which bypassed conditionals and risked `condition has length > 1` process crashes (DoS).
+**Learning:** `readline()` input representing exact integer choices (e.g. `1: Yes, 2: No`) must be validated using strictly bounded regex matching like `^[12]$`. Coercion functions (`as.integer()`) are not safe without prior bounding.
+**Prevention:** Always use strictly bounded regular expressions when validating exact interactive inputs to prevent unexpected NA coercion crashes.
diff --git a/DESCRIPTION b/DESCRIPTION
index f31d3e1..c90753c 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 6254651..918e19b 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-sentinel-validation.R b/tests/testthat/test-sentinel-validation.R
index 900f0ee..956c5c5 100644
--- a/tests/testthat/test-sentinel-validation.R
+++ b/tests/testthat/test-sentinel-validation.R
@@ -35,3 +35,64 @@ 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 input validation for readline protects against coercion DoS", {
+  # Mock interactive to TRUE to enter readline paths
+  mock_interactive <- mockery::mock(TRUE, TRUE, TRUE)
+  mockery::stub(aFIPC::autoFIPC, 'interactive', mock_interactive)
+
+  # 1. confirmCommonItems
+  mock_readline_confirm <- mockery::mock("99999999999999999999", "3", "invalid")
+  mockery::stub(aFIPC::autoFIPC, 'readline', mock_readline_confirm)
+
+  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"
+  )
+
+  # 2. oldformBILOGprior
+  mockery::stub(aFIPC::autoFIPC, 'interactive', mockery::mock(TRUE, TRUE, TRUE))
+  mockery::stub(aFIPC::autoFIPC, 'readline', mockery::mock("1")) # Pass confirmCommonItems
+
+  # Stub nested function call to simulate readline failures specifically for oldformBILOGprior
+  mock_readline_oldform <- mockery::mock("99999999999999999999", "3", "invalid")
+  mockery::stub(aFIPC::autoFIPC, 'readline', mock_readline_oldform, depth = 2) # checkoldformBILOGprior
+
+  expect_error(
+    aFIPC::autoFIPC(
+      newformXData = data.frame(A=1, B=2),
+      oldformYData = data.frame(A=1, B=2),
+      newformCommonItemNames = c('A'),
+      oldformCommonItemNames = c('A'),
+      confirmCommonItems = TRUE,
+      itemtype = "3PL"
+    ),
+    "Too many invalid oldform BILOG prior attempts"
+  )
+
+  # 3. newformBILOGprior
+  mock_readline_newform <- mockery::mock("99999999999999999999", "3", "invalid")
+  mockery::stub(aFIPC::autoFIPC, 'readline', mock_readline_newform, depth = 2)
+
+  # Need an oldFormModel so it reaches newform estimation
+  mock_old_model <- mirt::mirt(data.frame(A=c(1,0,1,0,1,0,1,0,1,0,1,0), B=c(0,1,0,1,0,1,0,1,0,1,0,1), C=c(1,1,0,0,1,1,0,0,1,1,0,0), D=c(0,0,1,1,0,0,1,1,0,0,1,1)), 1, itemtype="2PL", TOL=0.1, SE=FALSE, GenRandomPars=TRUE)
+
+  expect_error(
+    aFIPC::autoFIPC(
+      newformXData = data.frame(A=c(1,0,1,0,1,0,1,0,1,0,1,0), B=c(0,1,0,1,0,1,0,1,0,1,0,1), C=c(1,1,0,0,1,1,0,0,1,1,0,0), D=c(0,0,1,1,0,0,1,1,0,0,1,1)),
+      oldformYData = mock_old_model,
+      newformCommonItemNames = c('A'),
+      oldformCommonItemNames = c('A'),
+      confirmCommonItems = TRUE,
+      itemtype = "3PL",
+      oldformBILOGprior = TRUE
+    ),
+    "Too many invalid newform BILOG prior attempts"
+  )
+})