CVE-2025-6199: Gnome GdkPixbuf Information Disclosure Flaw

CVE-2025-6199 Overview

A flaw was found in the GIF parser of GdkPixbuf's LZW decoder. When an invalid symbol is encountered during decompression, the decoder sets the reported output size to the full buffer length rather than the actual number of written bytes. This logic error results in uninitialized sections of the buffer being included in the output, potentially leaking arbitrary memory contents in the processed image.

Critical Impact

This vulnerability allows attackers to craft malicious GIF files that, when processed by applications using GdkPixbuf, can leak uninitialized memory contents. This information disclosure could expose sensitive data from the application's memory space.

Affected Products

• GNOME GdkPixbuf 2.0.0
• Red Hat Enterprise Linux 6.0, 7.0, 8.0, 9.0, and 10.0
• Any application utilizing the affected GdkPixbuf library for GIF image processing

Discovery Timeline

• June 17, 2025 - CVE-2025-6199 published to NVD
• November 3, 2025 - Last updated in NVD database

Technical Details for CVE-2025-6199

Vulnerability Analysis

This vulnerability resides in GdkPixbuf's LZW (Lempel-Ziv-Welch) decoder, which is responsible for decompressing GIF image data. The flaw stems from improper handling of error conditions during the decompression process.

When the LZW decoder encounters an invalid symbol during decompression—a condition that can occur with malformed or maliciously crafted GIF files—it fails to correctly track the actual number of bytes written to the output buffer. Instead of reporting only the valid decompressed data, the decoder erroneously sets the output size to the total allocated buffer length.

This discrepancy means that subsequent operations treating the buffer as valid output data will process not only the legitimately decompressed bytes but also uninitialized memory regions. The uninitialized portions may contain residual data from previous allocations, potentially exposing sensitive information such as heap metadata, application state, or fragments of previously processed data.

Root Cause

The root cause is a logic error in the error handling path of the LZW decoder (CWE-200: Information Exposure). When an invalid symbol is detected, the decoder should terminate decompression and report only the bytes successfully written up to that point. However, the current implementation incorrectly reports the full buffer capacity as the output size, regardless of how many bytes were actually decompressed. This failure to properly track and report the actual written byte count leads to uninitialized memory being included in the processed image output.

Attack Vector

Exploitation requires local access with user interaction, as the victim must process a maliciously crafted GIF file. An attacker would:

1. Create a specially crafted GIF file containing an invalid LZW code sequence designed to trigger the error condition
2. Deliver the malicious GIF to the target system through various vectors (email attachment, web download, file share)
3. When a victim opens or previews the GIF using an application that relies on GdkPixbuf (such as GNOME-based image viewers, file managers, or thumbnail generators), the vulnerability is triggered
4. The resulting "processed image" contains leaked memory contents that could be extracted by the attacker

The vulnerability affects confidentiality but does not allow code execution or system integrity compromise.

Detection Methods for CVE-2025-6199

Indicators of Compromise

• Malformed GIF files with invalid LZW compression codes in the data stream
• Applications processing GIF images that produce unexpectedly large output buffers
• Anomalous image artifacts or data appended to processed GIF output that does not correspond to legitimate image content

Detection Strategies

• Monitor GIF file processing operations for files containing malformed LZW data streams
• Implement file integrity checking for applications that handle untrusted GIF images
• Use memory sanitizers (e.g., AddressSanitizer, MemorySanitizer) during development to detect uninitialized memory reads in GdkPixbuf-dependent applications
• Deploy file analysis tools to identify GIF files with structurally invalid LZW code tables

Monitoring Recommendations

• Review logs from image processing services for errors related to GIF decompression failures
• Monitor for unusual file access patterns involving GIF files from untrusted sources
• Track application crash reports that may indicate exploitation attempts against the LZW decoder

How to Mitigate CVE-2025-6199

Immediate Actions Required

• Update GdkPixbuf to the latest patched version provided by your distribution
• Apply security updates from Red Hat for affected Enterprise Linux versions
• Review and restrict processing of GIF files from untrusted sources in sensitive applications
• Consider disabling GIF support in GdkPixbuf if not required for your use case

Patch Information

Security advisories and patch information are available from multiple sources. The Red Hat CVE-2025-6199 Advisory provides guidance for Enterprise Linux systems. Additional details can be found in Red Hat Bug Report #2373147. Debian users should refer to the Debian LTS Announcement for package update information.

Workarounds

• Validate GIF files before processing using third-party validation tools
• Implement application-level sandboxing to isolate image processing operations from sensitive memory regions
• Use alternative image processing libraries that are not affected for handling untrusted GIF content
• Deploy content security policies to restrict GIF processing to trusted sources only