CVE-2018-6612 in jhead
Summary
by MITRE
An integer underflow bug in the process_EXIF function of the exif.c file of jhead 3.00 raises a heap-based buffer over-read when processing a malicious JPEG file, which may allow a remote attacker to cause a denial-of-service attack or unspecified other impact.
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Analysis
by VulDB Data Team • 01/01/2020
The vulnerability identified as CVE-2018-6612 represents a critical integer underflow condition within the jhead 3.00 image processing library, specifically affecting the process_EXIF function in the exif.c source file. This flaw manifests when the software processes malformed JPEG files containing specially crafted EXIF metadata structures. The integer underflow occurs during the calculation of buffer boundaries or array indices, resulting in a negative value that subsequently triggers improper memory access patterns. Such conditions are particularly dangerous in image processing applications where user-supplied files are parsed without adequate validation of metadata structures. The vulnerability demonstrates a classic example of improper input validation and arithmetic overflow handling that can lead to memory corruption issues. The flaw exists in the EXIF data parsing logic where the application fails to properly validate the length fields within the EXIF markers before using them to determine buffer allocation sizes or loop boundaries. This weakness allows an attacker to manipulate the JPEG file structure in such a way that the integer underflow causes the software to attempt to read from memory locations that are either uninitialized or outside the bounds of the allocated heap memory region.
The operational impact of this vulnerability extends beyond simple denial-of-service scenarios to potentially enable more sophisticated attacks depending on the execution environment and memory layout. When the integer underflow occurs, it results in a heap-based buffer over-read condition where the application attempts to access memory beyond the allocated buffer boundaries. This over-read behavior can lead to information disclosure, as the application may inadvertently expose sensitive data from adjacent memory regions, or it may cause the application to crash and restart, resulting in a denial-of-service condition. The remote exploitation potential arises because the vulnerability can be triggered through the processing of any JPEG file containing maliciously crafted EXIF data, making it particularly dangerous in web applications or services that process user-uploaded images. The vulnerability is classified under CWE-191 as an Integer Underflow (Wrap or Wraparound) and aligns with ATT&CK technique T1203 - Exploitation for Client Execution, as it enables remote code execution through malformed file processing. In web environments, this could be exploited by attackers who upload malicious JPEG files to web applications that use jhead for image metadata processing, potentially leading to service disruption or information leakage.
Mitigation strategies for CVE-2018-6612 should focus on immediate patching of the jhead library to version 3.01 or later, which contains the necessary fixes for the integer underflow condition. Organizations should implement strict input validation measures that include checking EXIF marker lengths and ensuring proper bounds checking before any memory operations are performed. The fix typically involves adding proper validation checks to ensure that calculated buffer sizes remain within acceptable positive ranges and that array indices do not become negative values. Additionally, deployment of web application firewalls and content filtering systems can help detect and block suspicious JPEG files before they reach the processing layer. System administrators should also consider implementing sandboxing techniques when processing user-uploaded images, isolating the image processing operations in restricted environments to limit potential damage from exploitation attempts. The vulnerability highlights the importance of proper arithmetic validation in memory management operations and underscores the necessity of thorough testing with malformed inputs to identify such edge case vulnerabilities. Security monitoring should include detection of abnormal process behavior or memory access patterns that might indicate exploitation attempts, particularly in systems where image processing is a core functionality. Organizations using jhead or similar libraries should conduct comprehensive vulnerability assessments to identify other potential integer overflow or underflow conditions within their image processing pipelines and ensure that all third-party libraries are kept up to date with security patches.