CVE-2019-11024 in libsixel
Summary
by MITRE
The load_pnm function in frompnm.c in libsixel.a in libsixel 1.8.2 has infinite recursion.
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Analysis
by VulDB Data Team • 08/27/2023
The vulnerability identified as CVE-2019-11024 resides within the libsixel library version 1.8.2, specifically within the load_pnm function located in the frompnm.c source file. This library is designed for converting image formats and handling various graphics file types including portable anymap format. The flaw manifests as infinite recursion when processing certain malformed or crafted pnm image files, creating a critical security risk that can be exploited by malicious actors.
The technical implementation of this vulnerability stems from inadequate input validation within the load_pnm function. When the function encounters specific patterns in pnm file structures, particularly those involving recursive references or malformed headers, it fails to properly terminate its recursive calls. This creates an unbounded recursion loop that consumes system resources and can lead to application crashes or denial of service conditions. The vulnerability is classified under CWE-674, which specifically addresses uncontrolled recursion, and represents a classic example of a stack overflow condition that can be triggered through crafted input data.
From an operational perspective, this vulnerability presents significant risks to systems that rely on libsixel for image processing, particularly in web applications, image conversion services, and terminal-based graphics applications. An attacker could exploit this weakness by uploading or providing maliciously crafted pnm files to systems using libsixel, potentially causing service disruption, system instability, or even complete application failure. The impact extends beyond simple denial of service as the infinite recursion can consume excessive CPU and memory resources, leading to resource exhaustion attacks that may affect system availability and performance.
The exploitation of CVE-2019-11024 aligns with ATT&CK technique T1499.004, which involves resource exhaustion attacks through manipulation of input data. This vulnerability demonstrates how seemingly benign image processing libraries can become attack vectors when they fail to properly validate input parameters and handle recursive data structures. Organizations using libsixel in production environments should consider this as a critical security concern, particularly those running applications that process untrusted image data. The vulnerability also relates to broader security principles around input validation and secure coding practices that emphasize the importance of bounded recursion and proper error handling in software components that process external data.
Mitigation strategies for this vulnerability include immediate patching of libsixel to version 1.8.3 or later, which contains the necessary fixes for the recursive call handling. System administrators should also implement input validation measures that restrict the types of image files accepted by applications using libsixel, and consider implementing resource limits and monitoring to detect potential exploitation attempts. Additionally, organizations should conduct thorough security assessments of their applications to identify other potential recursion vulnerabilities and establish proper testing procedures for input validation. The fix typically involves implementing proper termination conditions for recursive functions and adding bounds checking to prevent uncontrolled recursion patterns that could be triggered by malicious input data.