CVE-2020-35492: Cairographics Cairo Buffer Overflow Flaw

CVE-2020-35492 Overview

A stack buffer overflow vulnerability was discovered in Cairo's image-compositor.c component affecting all versions prior to 1.17.4. This flaw allows an attacker who can provide a crafted input file to Cairo's image compositor to cause a stack buffer overflow leading to an out-of-bounds write condition. Exploitation requires user interaction, such as convincing a user to open a malicious file in an application that uses Cairo for rendering, or when an application processes untrusted input through the Cairo library.

Critical Impact

This vulnerability enables attackers to achieve arbitrary code execution through stack buffer overflow, potentially leading to complete system compromise with full impact on confidentiality, integrity, and system availability.

Affected Products

• cairographics cairo (all versions prior to 1.17.4)

Discovery Timeline

• 2021-03-18 - CVE CVE-2020-35492 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-35492

Vulnerability Analysis

The vulnerability resides in Cairo's image compositor component (image-compositor.c), which is responsible for compositing and rendering graphical elements. Cairo is a widely-used 2D graphics library that provides device-independent output for various backends including X Window System, PDF, and PostScript.

The flaw is classified under CWE-121 (Stack-based Buffer Overflow) and CWE-787 (Out-of-bounds Write), indicating that the vulnerability allows writing data beyond the boundaries of an allocated stack buffer. This type of memory corruption vulnerability is particularly dangerous as it can be leveraged to overwrite critical stack data including return addresses, enabling arbitrary code execution.

The attack requires local access and user interaction—an attacker must craft a malicious input file and convince a victim to open it using an application that relies on Cairo for image processing. Once triggered, the out-of-bounds write can corrupt adjacent memory on the stack, potentially leading to control flow hijacking.

Root Cause

The root cause of this vulnerability is improper bounds checking in the image compositing routines within image-compositor.c. When processing specially crafted image data, the component fails to adequately validate the size of input data before copying it into a stack-allocated buffer. This allows attackers to provide input that exceeds the buffer's capacity, resulting in a stack buffer overflow and subsequent out-of-bounds memory writes.

Attack Vector

The attack vector is local, requiring user interaction to be exploited. An attacker would need to:

1. Craft a malicious image file or input that triggers the vulnerable code path in Cairo's image compositor
2. Deliver the malicious file to the victim (via email, web download, or other means)
3. Convince the victim to open the file using an application that utilizes Cairo for rendering

When the victim's application processes the malicious input through Cairo, the stack buffer overflow is triggered, allowing the attacker to write arbitrary data beyond the buffer boundaries. This can overwrite the function's return address or other critical stack data, enabling arbitrary code execution with the privileges of the vulnerable application.

Detection Methods for CVE-2020-35492

Indicators of Compromise

• Unexpected crashes in applications using Cairo library, particularly when processing image files
• Abnormal memory access patterns or segmentation faults in graphics rendering processes
• Evidence of exploitation attempts in application crash dumps showing stack corruption

Detection Strategies

• Monitor for crashes in applications linked against Cairo library versions prior to 1.17.4
• Implement memory protection mechanisms (ASLR, stack canaries) to detect and prevent exploitation attempts
• Use static analysis tools to identify applications in your environment that depend on vulnerable Cairo versions

Monitoring Recommendations

• Review system logs for repeated application crashes involving Cairo-dependent software
• Monitor for unusual file access patterns, particularly when users open untrusted image files
• Deploy endpoint detection solutions to identify potential exploitation of memory corruption vulnerabilities

How to Mitigate CVE-2020-35492

Immediate Actions Required

• Update Cairo to version 1.17.4 or later to remediate the vulnerability
• Audit systems to identify all applications that depend on Cairo and prioritize patching
• Implement user awareness training to reduce the risk of opening untrusted files
• Apply operating system-level memory protections (DEP, ASLR) if not already enabled

Patch Information

The vulnerability is resolved in Cairo version 1.17.4 and later. Organizations should update their Cairo installations to the latest available version. Additional details are available through the Red Hat Bug Report #1898396 and the Gentoo Security Advisory GLSA-202305-21.

Workarounds

• Restrict processing of untrusted image files in applications that use Cairo
• Implement application sandboxing to limit the impact of successful exploitation
• Consider disabling or removing applications that use vulnerable Cairo versions until patches can be applied
• Use input validation at the application layer to reject potentially malicious files before they reach the Cairo library

# Check installed Cairo version
pkg-config --modversion cairo

# On Debian/Ubuntu systems, update Cairo
sudo apt-get update && sudo apt-get install libcairo2

# On RHEL/CentOS systems
sudo yum update cairo

# On Gentoo systems
sudo emerge --sync && sudo emerge -av x11-libs/cairo