CVE-2020-36330: Libwebp Information Disclosure Flaw

CVE-2020-36330 Overview

A critical out-of-bounds read vulnerability was discovered in libwebp, a widely-used library for encoding and decoding WebP image files. The flaw exists in the ChunkVerifyAndAssign function within libwebp versions prior to 1.0.1. This vulnerability allows remote attackers to read memory beyond the intended buffer boundaries, potentially leading to sensitive data exposure and denial of service conditions.

The vulnerability is classified as CWE-125 (Out-of-Bounds Read) and affects a wide range of products that incorporate the libwebp library, including operating systems from Apple, Red Hat, and Debian, as well as enterprise software from NetApp.

Critical Impact

Remote attackers can exploit this out-of-bounds read vulnerability to access sensitive information from memory or crash affected applications, impacting both confidentiality and availability of affected systems.

Affected Products

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

Discovery Timeline

• 2021-05-21 - CVE CVE-2020-36330 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-36330

Vulnerability Analysis

This vulnerability stems from improper bounds checking in the ChunkVerifyAndAssign function within the libwebp library. When processing WebP image files, the function fails to properly validate chunk boundaries before reading data, allowing memory access beyond allocated buffers.

The out-of-bounds read condition can be triggered when parsing specially crafted WebP files that contain malformed chunk headers or size values. An attacker can leverage this flaw to read adjacent memory regions, potentially exposing sensitive data stored in memory or causing application crashes due to accessing invalid memory addresses.

The attack can be initiated remotely over a network without requiring any authentication or user interaction. When a vulnerable application processes a malicious WebP image—whether through web browsing, image preview, or file upload functionality—the out-of-bounds read is triggered. This makes web applications, image processing services, and mobile applications particularly susceptible to exploitation.

Root Cause

The root cause of CVE-2020-36330 lies in insufficient input validation within the ChunkVerifyAndAssign function. The function processes chunk data from WebP files without adequately verifying that the specified chunk sizes fall within the bounds of the allocated buffer. This allows chunk size values to exceed actual data boundaries, leading to out-of-bounds memory access during subsequent read operations.

The vulnerability is a direct result of trusting untrusted input data (chunk size fields from the WebP file format) without proper sanitization or boundary checks.

Attack Vector

The attack vector for this vulnerability is network-based. An attacker can exploit the vulnerability by:

1. Crafting a malicious WebP image file with manipulated chunk header values that specify sizes exceeding actual data boundaries
2. Delivering the malicious image to a target through various vectors such as websites, email attachments, messaging applications, or file uploads
3. When the victim's application attempts to parse the WebP image using a vulnerable version of libwebp, the ChunkVerifyAndAssign function reads beyond buffer boundaries
4. The out-of-bounds read results in either information disclosure (if the attacker can retrieve the read data) or denial of service through application crash

The exploitation mechanism centers on manipulating WebP chunk metadata. The WebP format uses a RIFF container with various chunk types. By providing malicious size values in chunk headers, an attacker forces the library to read beyond allocated memory regions. For detailed technical analysis, refer to the Red Hat Bug Report #1956853.

Detection Methods for CVE-2020-36330

Indicators of Compromise

• Unexpected application crashes or segmentation faults when processing WebP image files
• Memory access violations logged in system or application error logs related to libwebp operations
• Abnormal memory consumption patterns in applications handling WebP content
• Core dumps indicating out-of-bounds memory access in libwebp shared library

Detection Strategies

• Implement file integrity monitoring for libwebp library files and compare versions against known vulnerable releases (prior to 1.0.1)
• Deploy runtime application self-protection (RASP) solutions to detect out-of-bounds memory access attempts
• Monitor system logs for SIGSEGV or SIGBUS signals originating from processes using libwebp
• Use vulnerability scanning tools to identify systems running vulnerable libwebp versions

Monitoring Recommendations

• Configure application crash reporting to capture stack traces involving libwebp functions, particularly ChunkVerifyAndAssign
• Implement network monitoring to detect potentially malicious WebP files based on anomalous chunk structures
• Enable memory sanitizers (AddressSanitizer) in development and staging environments to catch out-of-bounds access attempts
• Monitor endpoint detection alerts for unusual behavior in applications that commonly process WebP images (browsers, image editors, messaging apps)

How to Mitigate CVE-2020-36330

Immediate Actions Required

• Update libwebp to version 1.0.1 or later across all affected systems
• Identify all applications and dependencies that include bundled versions of libwebp and prioritize updates
• Apply operating system security updates from Debian, Red Hat, and Apple that address this vulnerability
• Consider temporarily disabling WebP processing in critical applications until patches can be applied

Patch Information

Security patches addressing CVE-2020-36330 have been released by multiple vendors:

• libwebp: Update to version 1.0.1 or later from the WebM Project
• Debian: Security advisory DSA-4930 provides patched packages; see Debian Security Advisory DSA-4930
• Red Hat: Enterprise Linux 8.0 patches available via Red Hat Bug Report #1956853
• Apple: Security updates for iOS and iPadOS documented in Apple Support Article
• NetApp: Advisory and patches available at NetApp Security Advisory

Workarounds

• Implement input validation to reject WebP files from untrusted sources until patching is complete
• Use web application firewalls (WAF) to filter potentially malicious WebP uploads
• Consider using alternative image formats (PNG, JPEG) temporarily in high-risk environments
• Isolate WebP processing in sandboxed environments to limit potential impact from exploitation

# Check libwebp version on Linux systems
pkg-config --modversion libwebp

# Update libwebp on Debian/Ubuntu
sudo apt-get update && sudo apt-get install --only-upgrade libwebp6

# Update libwebp on RHEL/CentOS 8
sudo dnf update libwebp