CVE-2020-35521: Libtiff Memory Allocation DoS Vulnerability

CVE-2020-35521 Overview

A memory allocation failure vulnerability has been identified in libtiff, a widely-used library for reading and writing TIFF image files. The flaw exists in tif_read.c where a specially crafted TIFF file can trigger a memory allocation failure, causing the application to abort and resulting in a denial of service condition.

Critical Impact

Applications processing untrusted TIFF files may be forced to terminate unexpectedly, potentially disrupting services that rely on image processing functionality.

Affected Products

• LibTIFF (all versions prior to patch)
• Red Hat Enterprise Linux 7.0 and 8.0
• Fedora 33
• NetApp ONTAP Select Deploy Administration Utility

Discovery Timeline

• 2021-03-09 - CVE-2020-35521 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-35521

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the TIFF reading functionality within tif_read.c, where memory allocation operations are not properly validated.

When processing a maliciously crafted TIFF file, the library attempts to allocate memory based on values read from the file. If an attacker provides manipulated data that causes the memory allocation to fail, the library does not gracefully handle this error condition. Instead, the application aborts, leading to a denial of service.

This vulnerability requires local access to exploit, meaning an attacker must be able to provide a crafted TIFF file to a vulnerable application. User interaction is required as the victim must open or process the malicious file.

Root Cause

The root cause of this vulnerability stems from insufficient error handling during memory allocation operations in the TIFF reading code path. When tif_read.c processes image data, it allocates memory buffers based on dimensions and properties specified within the TIFF file structure. The code fails to properly validate these values before allocation and does not implement robust failure handling when the allocation fails.

This allows an attacker to craft a TIFF file with specific properties that cause the memory allocation to fail, triggering an unhandled abort condition rather than a graceful error return.

Attack Vector

The attack requires local access where an attacker provides a specially crafted TIFF file to a target system. The attack scenario involves:

1. An attacker creates a malicious TIFF file with manipulated header values designed to cause memory allocation failures
2. The victim opens the crafted TIFF file using an application that utilizes the vulnerable libtiff library
3. The libtiff library attempts to allocate memory based on the malformed file data
4. The memory allocation fails due to the crafted values
5. The application aborts, causing denial of service

The vulnerability affects the availability of the system but does not impact confidentiality or integrity, as no data is exposed or modified during exploitation.

Detection Methods for CVE-2020-35521

Indicators of Compromise

• Unexpected application crashes when processing TIFF image files
• Core dump files generated by applications that process TIFF images
• Log entries indicating memory allocation failures in image processing components
• Repeated process restarts for services handling TIFF file processing

Detection Strategies

• Monitor for abnormal termination signals in applications known to process TIFF files
• Implement file integrity monitoring on incoming TIFF files to detect anomalous file structures
• Deploy application crash detection for services utilizing libtiff
• Audit system logs for repeated crashes correlated with TIFF file processing activities

Monitoring Recommendations

• Enable core dump analysis for applications using libtiff to capture crash evidence
• Monitor memory allocation patterns in image processing applications for anomalies
• Implement alerting on service restarts for TIFF-processing applications
• Track file access patterns for unusual TIFF file processing activity

How to Mitigate CVE-2020-35521

Immediate Actions Required

• Update libtiff to the latest patched version available from your distribution
• Restrict access to TIFF file upload and processing functionality to trusted users
• Implement input validation for TIFF files before processing with libtiff
• Consider using sandboxed environments for processing untrusted image files

Patch Information

Security patches are available from various distribution vendors. For detailed patch information, consult the following vendor advisories:

• Red Hat Bug Report #1932034 - Official Red Hat bug tracking and patch information
• Fedora Package Announcement - Fedora security update announcement
• Gentoo GLSA 202104-06 - Gentoo Linux Security Advisory
• NetApp Security Advisory NTAP-20210521-0009 - NetApp product advisory

Apply updates according to your distribution's package management system.

Workarounds

• Isolate TIFF processing applications in sandboxed or containerized environments to limit impact
• Implement file size and dimension validation before passing TIFF files to libtiff
• Restrict TIFF file processing to known-good sources until patches can be applied
• Deploy process monitoring to automatically restart crashed services as a temporary measure

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

# Example: Update libtiff on Fedora systems
sudo dnf update libtiff

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