diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 8b7813b..0e56ff5 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -9,3 +9,7 @@
 5. DoS 완화를 위해 `return(1L)` 같은 기본 승인값을 넣을 때는 추정 기준척도, anchor/common item, true parameter 재현 계약을 우회하지 않는지 먼저 검증합니다.
 6. Fail-secure 에러 메시지는 테스트의 일부로 취급합니다. 보안 테스트는 실제 구현 메시지와 맞아야 하며, 오래된 `"Interactive prompt is not available"` 같은 별도 문구를 새로 만들지 않습니다.
 7. Prompt DoS 회귀 테스트는 모델 추정 실패에 기대지 말고, common-item confirmation guard처럼 취약한 입력 경계에서 바로 발생하는 fail-secure 에러를 검증합니다.
+## 2024-07-03 - [Preventing Denial of Service (DoS) with Infinite Retries]
+**Vulnerability:** Found unbounded `while (!exists('var'))` loops used alongside `try()` inside `R/aFIPC.R`. If the operation inside `try()` consistently fails, this creates an infinite loop resulting in a Denial of Service.
+**Learning:** `try()` constructs combined with existence checks on the assigned variable are a common but risky pattern for retrying flaky procedures like parameter estimation in R. Without bounds, these loops will block the process forever on unrecoverable failures.
+**Prevention:** Always include a `max_retries` counter in retry loops. If `max_retries` is exhausted, explicitly stop execution with `stop("Max retries reached")`.
diff --git a/R/aFIPC.R b/R/aFIPC.R
index d0329f2..2325f2a 100644
--- a/R/aFIPC.R
+++ b/R/aFIPC.R
@@ -216,7 +216,10 @@ autoFIPC <-
           )
 
           try(rm(oldFormModel))
-          while (!exists('oldFormModel')) {
+          max_retries <- 5
+          retries <- 0
+          while (!exists('oldFormModel') && retries < max_retries) {
+            retries <- retries + 1
             try(
               oldFormModel <-
                 mirt::mirt(
@@ -231,6 +234,9 @@ autoFIPC <-
                 )
             )
           }
+          if (!exists('oldFormModel')) {
+            stop("oldFormModel estimation failed after maximum retries.")
+          }
         }
       }
 
@@ -428,7 +434,10 @@ autoFIPC <-
           )
 
           try(rm(newFormModel))
-          while (!exists('newFormModel')) {
+          max_retries <- 5
+          retries <- 0
+          while (!exists('newFormModel') && retries < max_retries) {
+            retries <- retries + 1
             try(
               newFormModel <-
                 mirt::mirt(
@@ -443,6 +452,9 @@ autoFIPC <-
                 )
             )
           }
+          if (!exists('newFormModel')) {
+            stop("newFormModel estimation failed after maximum retries.")
+          }
         }
       }