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ctf/docker/pwn/bof-basic/vuln.c

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+/*
+ * T3MP3ST CTF - Buffer Overflow Challenge
+ *
+ * Vulnerability: Stack buffer overflow in vuln()
+ * Protections: None (no canary, no PIE, NX disabled)
+ * Objective: Redirect execution to win() function
+ *
+ * DO NOT USE IN PRODUCTION - Intentionally vulnerable
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+// Disable buffering
+void setup() {
+    setvbuf(stdin, NULL, _IONBF, 0);
+    setvbuf(stdout, NULL, _IONBF, 0);
+    setvbuf(stderr, NULL, _IONBF, 0);
+}
+
+// Win function - prints the flag
+void win() {
+    FILE *f = fopen("/challenge/flag.txt", "r");
+    if (f == NULL) {
+        printf("Error: Could not open flag file\n");
+        return;
+    }
+
+    char flag[128];
+    if (fgets(flag, sizeof(flag), f) != NULL) {
+        printf("\n[+] ACCESS GRANTED\n");
+        printf("[+] FLAG: %s\n", flag);
+    }
+    fclose(f);
+    exit(0);
+}
+
+// Vulnerable function
+void vuln() {
+    char buffer[64];
+
+    printf("╔════════════════════════════════════════╗\n");
+    printf("║     SECURE TERMINAL ACCESS SYSTEM      ║\n");
+    printf("╚════════════════════════════════════════╝\n");
+    printf("\nEnter access code: ");
+
+    // VULNERABLE: gets() does not check buffer bounds
+    gets(buffer);
+
+    printf("\nAccess code received: %s\n", buffer);
+    printf("[-] ACCESS DENIED\n");
+}
+
+int main() {
+    setup();
+
+    printf("\n[*] Terminal initialized\n");
+    printf("[*] win() function at: %p\n", win);  // Hint for players
+
+    vuln();
+
+    return 0;
+}