CVE-2020-36328: Libwebp Buffer Overflow Vulnerability

CVE-2020-36328 Overview

A heap-based buffer overflow vulnerability was discovered in libwebp versions before 1.0.1. The flaw exists in the WebPDecodeRGBInto function due to an invalid check for buffer size. This vulnerability allows remote attackers to potentially execute arbitrary code, cause denial of service, or compromise data confidentiality and integrity by crafting malicious WebP image files that trigger the buffer overflow condition during decoding operations.

Critical Impact

This heap-based buffer overflow vulnerability poses the highest threat to data confidentiality, integrity, and system availability. Remote attackers can exploit this flaw without authentication by delivering maliciously crafted WebP images through web content, email attachments, or other file sharing mechanisms.

Affected Products

• webmproject libwebp (versions before 1.0.1)
• Red Hat Enterprise Linux 7.0 and 8.0
• NetApp ONTAP Select Deploy Administration Utility
• Debian Linux 9.0 and 10.0
• Apple iPadOS 14.7
• Apple iPhone OS 14.7

Discovery Timeline

• 2021-05-21 - CVE CVE-2020-36328 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-36328

Vulnerability Analysis

The vulnerability stems from improper buffer size validation in the WebPDecodeRGBInto function within the libwebp library. When processing WebP image data, the function fails to adequately verify that the destination buffer has sufficient capacity to hold the decoded RGB pixel data. This oversight allows an attacker to craft a specially designed WebP image where the declared dimensions or pixel data exceed the allocated buffer space.

The libwebp library is widely deployed across operating systems and applications for WebP image format support, making this vulnerability particularly impactful. The flaw is classified as CWE-787 (Out-of-bounds Write), indicating that the vulnerability allows writing data beyond the boundaries of allocated memory regions.

Root Cause

The root cause of CVE-2020-36328 is an invalid check for buffer size in the WebPDecodeRGBInto function. The function accepts a user-provided output buffer and its size as parameters, but the validation logic contains a flaw that permits certain buffer size values to pass the check even when they are insufficient for the decoded image data. This allows heap memory to be corrupted with attacker-controlled data when processing malicious WebP files.

Attack Vector

The attack is network-exploitable and requires no authentication or user interaction beyond standard image rendering. Exploitation scenarios include:

1. Web-based attacks: Embedding malicious WebP images in web pages that are rendered by vulnerable browsers or applications
2. Email-based attacks: Sending malicious WebP attachments that trigger the vulnerability when previewed
3. Document-based attacks: Embedding crafted WebP images in documents processed by vulnerable applications
4. Messaging applications: Transmitting malicious images through messaging platforms that decode WebP content

The vulnerability can be exploited when any application using the vulnerable libwebp library attempts to decode a crafted WebP image into an RGB buffer using the WebPDecodeRGBInto function. The attacker can overflow the heap buffer, potentially overwriting adjacent memory structures to achieve code execution or cause application crashes.

Detection Methods for CVE-2020-36328

Indicators of Compromise

• Unexpected application crashes when processing WebP image files, particularly with error messages referencing heap corruption or memory access violations
• Anomalous memory allocation patterns in applications that process WebP content
• Presence of unusually large or malformed WebP files with suspicious dimension metadata
• Core dumps or crash reports indicating heap overflow in libwebp-related functions

Detection Strategies

• Monitor application logs for crashes related to image decoding operations, especially those involving WebP formats
• Implement file integrity monitoring for WebP images with anomalous header values or size discrepancies
• Deploy memory safety tools such as AddressSanitizer in development and testing environments to detect heap overflows
• Use intrusion detection systems to identify network traffic containing potentially malicious WebP images with unusual characteristics

Monitoring Recommendations

• Enable detailed crash reporting for applications that process image content to identify potential exploitation attempts
• Monitor system memory usage for unexpected spikes during image processing operations
• Implement application-level logging for WebP decoding functions to track error conditions
• Review security advisories from affected vendors including Red Hat Bug Report and Apple Support Article

How to Mitigate CVE-2020-36328

Immediate Actions Required

• Update libwebp to version 1.0.1 or later immediately on all affected systems
• Apply vendor-specific patches for affected operating systems including Red Hat Enterprise Linux, Debian Linux, and Apple iOS/iPadOS
• Audit systems to identify all applications that depend on libwebp for WebP image processing
• Consider temporarily disabling WebP image processing in critical applications if immediate patching is not feasible

Patch Information

Security patches have been released by multiple vendors to address this vulnerability:

• libwebp: Upgrade to version 1.0.1 or later from the WebM Project
• Red Hat Enterprise Linux: Apply security updates as documented in the Red Hat Bug Report
• Debian Linux: Apply updates per Debian Security Announcement DSA-4930 and the Debian LTS Advisory #00005
• Apple iOS/iPadOS: Update to versions that include the fix as noted in the Apple Support Article
• NetApp: Review the NetApp Security Advisory for ONTAP Select Deploy Administration Utility updates

Workarounds

• Disable WebP image processing capabilities in applications where the feature is not essential until patches can be applied
• Implement input validation to reject WebP files with suspicious or invalid dimension metadata before processing
• Use web application firewalls or content filtering to block potentially malicious WebP images from reaching vulnerable systems
• Isolate applications that must process untrusted WebP content using sandboxing or containerization technologies

# Configuration example - Check libwebp version on Linux systems
dpkg -l libwebp* 2>/dev/null || rpm -qa | grep libwebp

# Verify libwebp version meets minimum requirement (1.0.1+)
webpinfo -version 2>/dev/null || echo "webpinfo not available, check package manager"

# For Debian/Ubuntu systems, update libwebp
sudo apt update && sudo apt upgrade libwebp6 libwebp-dev

# For RHEL/CentOS systems, update libwebp
sudo yum update libwebp