diff --git a/.changeset/sentinel-dos-fix.md b/.changeset/sentinel-dos-fix.md
new file mode 100644
index 00000000..8974adc7
--- /dev/null
+++ b/.changeset/sentinel-dos-fix.md
@@ -0,0 +1,5 @@
+---
+"node-version": patch
+---
+
+Fix: Add DoS protection by limiting version string length in comparison methods.
diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 356c7f03..d7f38753 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -2,3 +2,8 @@
 **Vulnerability:** The version comparison logic in `src/index.ts` failed to correctly parse version strings prefixed with `v` (e.g., `"v10.0.0"`). The `Number()` function would return `NaN` for segments like `"v10"`, leading to incorrect comparison results (often evaluating as equal due to `NaN` comparison behavior).
 **Learning:** Naive number parsing of version strings can be dangerous. Standard semver libraries handle this, but custom implementations must be careful. Specifically, `NaN` in comparisons can lead to "fail open" scenarios where a lower version is considered "at least" a higher version because the check returns false for both `<` and `>`, falling through to equality or default cases.
 **Prevention:** Always sanitize version strings (strip non-numeric prefixes) before parsing. When implementing custom version comparison, handle `NaN` explicitly or use a robust library. Ensure inputs are validated or normalized.
+
+## 2026-01-15 - [DoS via Long Version Strings]
+**Vulnerability:** The `compareTo` function lacked input length validation, exposing the application to Denial of Service (DoS) attacks via excessively long version strings that consume CPU and memory during parsing (e.g., `trim`, `split`).
+**Learning:** Seemingly harmless string operations can become vectors for resource exhaustion if input size is unchecked.
+**Prevention:** Enforce strict maximum length limits (e.g., `MAX_VERSION_LENGTH`) on all user-controlled inputs before processing them.
diff --git a/src/index.ts b/src/index.ts
index 625ca808..8dc26027 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -9,6 +9,11 @@ import type { NodeVersion } from "./types.js";
 
 export type { NodeVersion };
 
+/**
+ * Maximum length for a version string to prevent ReDoS/DoS attacks.
+ */
+const MAX_VERSION_LENGTH = 256;
+
 /**
  * End-of-Life dates for Node.js major versions.
  */
@@ -52,6 +57,10 @@ export const getVersion = (): NodeVersion => {
      * Compare the current node version with a target version string.
      */
     const compareTo = (target: string): number => {
+        if (target.length > MAX_VERSION_LENGTH) {
+            return NaN;
+        }
+
         if (target !== target.trim() || target.length === 0) {
             return NaN;
         }
diff --git a/src/security.test.ts b/src/security.test.ts
index b5942fd7..b9e97b45 100644
--- a/src/security.test.ts
+++ b/src/security.test.ts
@@ -63,4 +63,10 @@ describe("security fixes", () => {
         const v = getVersion();
         expect(v.isAtLeast("10.0.0")).toBe(true);
     });
+
+    test("should reject excessively long version strings (DoS prevention)", () => {
+        const v = getVersion();
+        const longVersion = `1.${"0.".repeat(200)}1`;
+        expect(v.isAtLeast(longVersion)).toBe(false);
+    });
 });