CVE-2026-4738: OSGeo GDAL Buffer Overflow Vulnerability

CVE-2026-4738 Overview

CVE-2026-4738 is a critical memory buffer vulnerability affecting OSGeo GDAL, specifically within the frmts/zlib/contrib/infback9 modules. This Improper Restriction of Operations within the Bounds of a Memory Buffer vulnerability (CWE-119) exists in the inftree9.C program file and affects GDAL versions prior to 3.11.0. The vulnerability allows attackers to perform operations that exceed the boundaries of allocated memory buffers, potentially leading to memory corruption, code execution, or system compromise.

Critical Impact

This network-accessible vulnerability in GDAL's zlib decompression modules could allow remote attackers to trigger memory corruption through specially crafted input, potentially resulting in arbitrary code execution with high impact to confidentiality, integrity, and availability.

Affected Products

• OSGeo GDAL versions before 3.11.0
• Applications utilizing GDAL's frmts/zlib/contrib/infback9 modules
• Systems processing geospatial data through vulnerable GDAL installations

Discovery Timeline

• 2026-03-24 - CVE CVE-2026-4738 published to NVD
• 2026-03-24 - Last updated in NVD database

Technical Details for CVE-2026-4738

Vulnerability Analysis

This vulnerability stems from improper boundary checking within GDAL's embedded zlib decompression functionality, specifically in the infback9 module used for deflate64 decompression. The inftree9.C file contains code responsible for building Huffman tables during decompression operations. When processing malformed or specially crafted compressed data, the code fails to properly validate buffer boundaries before performing memory operations.

The vulnerability is network-accessible and requires user interaction (such as opening a malicious file), but has no authentication requirements. The flaw can impact not only the vulnerable component but potentially affect downstream systems that rely on GDAL for geospatial data processing. The confirmed active exploitation status and the potential for subsequent system compromise elevate the risk profile significantly.

Root Cause

The root cause lies in CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer. The inftree9.C module lacks adequate bounds checking when constructing Huffman decoding tables during deflate64 decompression. This allows memory operations to occur outside the intended buffer boundaries when processing crafted input data, leading to buffer overflow conditions.

Attack Vector

The attack vector is network-based, requiring an attacker to deliver malicious content to a victim. Exploitation scenarios include:

1. A victim opening a maliciously crafted geospatial file (GeoTIFF, JPEG2000, or other GDAL-supported formats) that contains compressed data processed by the vulnerable infback9 module
2. Web applications using GDAL to process user-uploaded geospatial data
3. Automated data pipelines ingesting untrusted geospatial datasets

The vulnerability in the zlib decompression module is triggered when GDAL attempts to decompress the malformed data stream, causing out-of-bounds memory access during Huffman table construction.

Detection Methods for CVE-2026-4738

Indicators of Compromise

• Unexpected crashes or segmentation faults in applications using GDAL when processing geospatial files
• Abnormal memory allocation patterns or memory corruption errors in GDAL-dependent processes
• Core dumps or crash logs referencing inftree9.C or the infback9 module

Detection Strategies

• Monitor for crashes in GDAL-dependent applications, particularly those involving file decompression operations
• Implement file integrity monitoring on systems processing untrusted geospatial data
• Deploy endpoint detection and response (EDR) solutions capable of detecting memory corruption exploitation attempts

Monitoring Recommendations

• Enable crash reporting and analysis for applications utilizing GDAL libraries
• Monitor process behavior for anomalous memory access patterns in geospatial processing workflows
• Review application logs for decompression errors or unexpected terminations when handling compressed geospatial data

How to Mitigate CVE-2026-4738

Immediate Actions Required

• Upgrade OSGeo GDAL to version 3.11.0 or later immediately
• Restrict processing of untrusted geospatial files until patching is complete
• Implement network segmentation to isolate systems running vulnerable GDAL versions
• Review and audit any web applications or services that accept user-uploaded geospatial data

Patch Information

OSGeo has addressed this vulnerability in GDAL version 3.11.0. The fix is available through GitHub PR #12244 for GDAL, which implements proper bounds checking in the inftree9.C module. Organizations should prioritize updating to GDAL 3.11.0 or applying the specific patch from the referenced pull request.

Workarounds

• Disable or restrict access to functionality that processes compressed geospatial data through the infback9 module if upgrading is not immediately feasible
• Implement strict input validation and sanitization for all geospatial files before processing with GDAL
• Use application sandboxing or containerization to limit the impact of potential exploitation
• Deploy web application firewalls (WAF) to filter potentially malicious uploads targeting geospatial processing endpoints