CVE-2020-36331: Webmproject Libwebp DOS Vulnerability

CVE-2020-36331 Overview

CVE-2020-36331 is an out-of-bounds read vulnerability discovered in libwebp, the WebP image codec library maintained by the WebM Project. This memory corruption flaw exists in the ChunkAssignData function in versions prior to 1.0.1. When processing maliciously crafted WebP image files, the vulnerable function can read beyond allocated memory boundaries, potentially exposing sensitive data or causing application crashes.

The vulnerability poses a significant risk due to the widespread adoption of libwebp across multiple operating systems and platforms, including Apple iOS, iPadOS, Red Hat Enterprise Linux, and Debian Linux distributions. Attackers could exploit this flaw through malicious WebP images delivered via web content, email attachments, or other image-processing workflows.

Critical Impact

This out-of-bounds read vulnerability threatens data confidentiality through potential memory disclosure and service availability through denial of service conditions. Given libwebp's integration into web browsers and operating systems, exploitation could affect millions of devices.

Affected Products

• webmproject libwebp (versions before 1.0.1)
• redhat enterprise_linux 8.0
• netapp ontap_select_deploy_administration_utility
• debian debian_linux 9.0 and 10.0
• apple ipados
• apple iphone_os

Discovery Timeline

• 2021-05-21 - CVE CVE-2020-36331 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-36331

Vulnerability Analysis

This vulnerability is classified as CWE-125 (Out-of-Bounds Read), a memory corruption issue that occurs when software reads data past the end or before the beginning of an allocated buffer. In the context of CVE-2020-36331, the ChunkAssignData function in libwebp fails to properly validate buffer boundaries when processing WebP image chunk data.

The flaw can be triggered remotely through the network when a victim application processes a maliciously crafted WebP image. No authentication or user privileges are required to exploit this vulnerability, making it accessible to unauthenticated attackers. While the vulnerability does not allow arbitrary code execution or data modification, it can lead to information disclosure from process memory and denial of service through application crashes.

Root Cause

The root cause of CVE-2020-36331 lies in improper bounds checking within the ChunkAssignData function. When parsing WebP image chunks, the function fails to adequately validate that read operations remain within the bounds of allocated memory buffers. This oversight allows specially crafted input data to trigger reads past the allocated buffer, accessing adjacent memory regions that may contain sensitive information or unmapped memory pages.

The WebP format uses a RIFF container with various chunk types (VP8, VP8L, ALPH, etc.), and the vulnerability manifests during the chunk assignment process where data pointers and sizes are not properly validated against actual buffer boundaries.

Attack Vector

The attack vector for CVE-2020-36331 is network-based, requiring no privileges or user interaction beyond the target application processing a malicious WebP image. Exploitation scenarios include:

1. Web-based attacks: Embedding malicious WebP images in web pages that are rendered by browsers using vulnerable libwebp versions
2. Email attachments: Sending crafted WebP files that are processed by email clients or preview handlers
3. Document processing: Including malicious WebP images in documents that trigger automatic thumbnail generation or preview rendering
4. Content delivery: Serving malicious images through CDNs or image hosting services

The vulnerability mechanism exploits the ChunkAssignData function's failure to validate memory boundaries. When processing a WebP file with malformed chunk metadata, the function may attempt to read beyond the allocated buffer. This out-of-bounds access can expose sensitive heap memory contents or trigger a crash when accessing unmapped memory pages. For detailed technical analysis, refer to the Red Hat Bug Report #1956856.

Detection Methods for CVE-2020-36331

Indicators of Compromise

• Unexpected application crashes in software that processes WebP images, particularly with stack traces referencing ChunkAssignData or related libwebp functions
• Memory access violation errors logged during image processing operations
• Abnormal memory consumption patterns in applications handling WebP content
• Core dumps or crash reports from image rendering components

Detection Strategies

• Deploy memory safety monitoring tools to detect out-of-bounds read attempts in processes using libwebp
• Implement application-level logging for WebP parsing errors and exceptions
• Use SentinelOne's behavioral AI engine to detect exploitation attempts targeting memory corruption vulnerabilities
• Monitor for unusual patterns in WebP image processing, such as repeated crashes from specific image sources

Monitoring Recommendations

• Configure crash reporting systems to alert on libwebp-related failures
• Implement network-based monitoring for unusual WebP file characteristics in incoming traffic
• Deploy endpoint detection solutions capable of identifying memory corruption exploitation patterns
• Monitor system logs for segmentation faults and memory access violations in image-processing applications

How to Mitigate CVE-2020-36331

Immediate Actions Required

• Upgrade libwebp to version 1.0.1 or later immediately across all affected systems
• Audit all applications and systems for bundled or statically linked vulnerable libwebp versions
• Apply vendor-specific patches from Red Hat, Debian, Apple, and NetApp as applicable to your environment
• Consider temporarily blocking or sandboxing WebP image processing until patches are deployed

Patch Information

Multiple vendors have released security updates to address CVE-2020-36331. The primary fix is available in libwebp version 1.0.1 and later. Administrators should consult the following vendor advisories for platform-specific patching guidance:

• Red Hat Bug Report #1956856 - Red Hat Enterprise Linux patches
• Debian Security Advisory DSA-4930 - Debian security updates
• Apple Support Article HT212601 - iOS and iPadOS updates
• NetApp Security Advisory NTAP-20211112-0001 - ONTAP Select patches
• Debian LTS Advisory June 2021 - Debian LTS updates

Workarounds

• Disable or restrict WebP image processing in web browsers and applications where feasible until patches can be applied
• Implement content filtering to block WebP files from untrusted sources at network perimeters
• Use application sandboxing to limit the impact of potential exploitation in image-processing workflows
• Deploy web application firewalls with rules to detect malformed WebP content

# Verify installed libwebp version on Linux systems
dpkg -l libwebp* 2>/dev/null || rpm -qa | grep -i libwebp

# Check for vulnerable versions (versions below 1.0.1 are affected)
webpinfo -version 2>/dev/null || echo "webpinfo not available, check package manager"

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

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