CVE-2020-35523: Libtiff Integer Overflow RCE Vulnerability

CVE-2020-35523 Overview

An integer overflow vulnerability was discovered in the libtiff library, specifically within the tif_getimage.c file. This flaw allows an attacker to inject and execute arbitrary code when a user opens a specially crafted TIFF image file. The vulnerability poses significant threats to confidentiality, integrity, and system availability, as successful exploitation could lead to complete system compromise.

Critical Impact

Arbitrary code execution through crafted TIFF files can lead to full system compromise, data exfiltration, and persistent attacker access.

Affected Products

• libtiff (all vulnerable versions prior to patch)
• Debian Linux 9.0 and 10.0
• Red Hat Enterprise Linux 6.0, 7.0, and 8.0
• NetApp ONTAP Select Deploy Administration Utility

Discovery Timeline

• 2021-03-09 - CVE-2020-35523 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-35523

Vulnerability Analysis

The vulnerability exists in the image processing functionality of the libtiff library, specifically in the tif_getimage.c source file. When processing TIFF image files, the library performs calculations that can result in an integer overflow condition. This occurs when arithmetic operations on image dimension values or buffer sizes exceed the maximum value that can be stored in the integer data type, causing the value to wrap around to a smaller number.

The integer overflow leads to improper memory allocation, where a smaller-than-expected buffer is allocated. Subsequent write operations then overflow this undersized buffer, allowing an attacker to corrupt adjacent memory regions. This memory corruption primitive can be leveraged to achieve arbitrary code execution.

Since this vulnerability requires local access and user interaction (opening a malicious TIFF file), exploitation typically occurs through social engineering vectors such as email attachments, malicious downloads, or compromised websites serving crafted image files.

Root Cause

The root cause is an Integer Overflow vulnerability (CWE-190) in the tif_getimage.c file within the libtiff library. The code fails to properly validate and handle large integer values during image processing calculations, allowing arithmetic operations to overflow and produce unexpected results. This lack of integer boundary checking before memory allocation operations creates an exploitable condition.

Attack Vector

The attack requires local access to the target system with no privileges required. However, user interaction is necessary—the victim must open a maliciously crafted TIFF file. Attack scenarios include:

1. Email-based attacks: Sending crafted TIFF files as email attachments
2. Web-based attacks: Hosting malicious TIFF files on compromised or attacker-controlled websites
3. Document embedding: Embedding malicious TIFF images in documents processed by applications using libtiff
4. Supply chain attacks: Compromising image repositories or build systems to include malicious TIFF files

When a vulnerable application processes the crafted TIFF file, the integer overflow triggers memory corruption, enabling the attacker to execute arbitrary code with the privileges of the user running the application.

The vulnerability is triggered during image processing operations in tif_getimage.c. When crafted image dimension values cause integer overflow during buffer size calculations, the resulting undersized allocation leads to heap-based memory corruption. Technical details of the fix can be found in the GitLab Merge Request #160.

Detection Methods for CVE-2020-35523

Indicators of Compromise

• Unexpected application crashes when processing TIFF image files
• Anomalous memory allocation patterns in applications using libtiff
• Presence of TIFF files with abnormally large or suspicious dimension values in image metadata
• Signs of code execution or shell spawning from image processing applications

Detection Strategies

• Monitor for crashes or exceptions in applications that process TIFF files, particularly those linked against libtiff
• Implement file integrity monitoring for system libraries to detect unauthorized modifications
• Use endpoint detection and response (EDR) solutions to identify exploitation attempts through behavioral analysis
• Scan systems for vulnerable versions of libtiff using vulnerability management tools

Monitoring Recommendations

• Enable detailed logging for applications that process image files
• Configure alerts for unusual process behavior following TIFF file access
• Monitor network traffic for suspicious TIFF file downloads from untrusted sources
• Implement application allowlisting to prevent unauthorized code execution

How to Mitigate CVE-2020-35523

Immediate Actions Required

• Update libtiff to the patched version immediately on all affected systems
• Restrict processing of TIFF files from untrusted sources until patches are applied
• Implement network-level blocking of TIFF file downloads from unknown sources
• Review and update any containerized applications or deployments using vulnerable libtiff versions

Patch Information

The vulnerability has been addressed through a code commit in the libtiff project. The fix adds proper integer overflow checks before memory allocation operations to prevent the exploitable condition.

Patch Details:

• Commit: GitLab Commit c8d613e
• Merge Request: GitLab Merge Request #160

Distribution-Specific Patches:

• Debian: Security Advisory DSA-4869
• Red Hat: Bug Report ID 1932040
• Gentoo: GLSA 202104-06
• NetApp: Security Advisory NTAP-20210521-0009

Workarounds

• Disable or restrict applications that process TIFF files until patching is complete
• Use application sandboxing to limit the impact of potential exploitation
• Implement strict input validation for TIFF files before processing
• Consider using alternative image processing libraries for critical systems until updates are applied

# Example: Update libtiff on Debian/Ubuntu systems
sudo apt-get update
sudo apt-get install --only-upgrade libtiff5 libtiff-tools

# Example: Update libtiff on RHEL/CentOS systems
sudo yum update libtiff

# Verify installed version after patching
dpkg -l | grep libtiff    # Debian/Ubuntu
rpm -qa | grep libtiff    # RHEL/CentOS