CVE-2026-116724 in FLTK
Summary
by MITRE • 10/27/2026
FLTK through 1.4.5 contains an integer overflow vulnerability in Fl_BMP_Image::load_bmp_() that causes undersized pixel buffer allocation from file-supplied width and height. Attackers can supply a crafted BMP or ICO file with large dimensions so row decoding writes file-derived data past the heap buffer, corrupting the application heap.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 10/27/2026
The FLTK library, specifically through version 1.4.5, contains a critical integer overflow vulnerability within the Fl_BMP_Image::load_bmp_() function that poses significant risks to applications relying on this toolkit for graphical user interface rendering and image processing. This flaw stems from an improper handling of dimension parameters when parsing Bitmap (BMP) or Icon (ICO) files. When the library processes these file formats, it extracts width and height values directly from the file header without sufficient validation against integer limits before performing arithmetic operations to calculate buffer sizes. Specifically, the calculation for the required pixel buffer size involves multiplying dimensions which can result in an integer overflow if the input values are sufficiently large or crafted maliciously. This mathematical error leads to a significantly smaller allocation than what is actually needed to store the image data safely.
The core technical flaw lies in the failure to detect when the multiplication of width and height exceeds the maximum value representable by the integer type used for memory allocation sizing. In many systems, this results in the allocated heap buffer being drastically undersized relative to the actual amount of pixel data that needs to be written during the decoding process. As the library proceeds to decode the image rows from the file-supplied width and height, it writes data into the pre-allocated buffer without bounds checking against the true size requirements derived from the original dimensions. Consequently, subsequent write operations extend beyond the boundaries of the allocated heap memory block. This out-of-bounds write corrupts adjacent heap metadata or other in-use allocations, leading to undefined behavior within the application runtime environment.
The operational impact of this vulnerability is severe and multifaceted. An attacker can exploit this condition by supplying a specially crafted BMP or ICO file containing large dimension values that trigger the integer overflow during buffer size calculation. Upon loading such a file, the resulting heap corruption can lead to various detrimental outcomes depending on the specific memory layout and execution context. These outcomes include application crashes due to segmentation faults when accessing corrupted pointers, data leakage if sensitive information stored in adjacent memory is exposed through subsequent reads, or potentially arbitrary code execution if an attacker can precisely control the overwritten heap metadata to redirect function pointers or object vtables. This makes the vulnerability particularly dangerous for applications that accept user-uploaded images or process untrusted image sources without rigorous sanitization prior to loading them into FLTK components.
From a classification perspective, this vulnerability aligns with CWE-190 Integer Overflow or Wraparound and CWE-787 Out-of-bounds Write. The exploitation technique involves manipulating input data to cause an arithmetic error that results in insufficient resource allocation, which is characteristic of CWE-672 Use of Operationally Unsafe Default. In terms of the MITRE ATT&CK framework, this vulnerability facilitates initial access or privilege escalation depending on the context, falling under techniques related to memory corruption exploitation such as T1203 Exploitation for Client Execution if used in a client-side attack scenario where an attacker tricks a user into opening a malicious image file. The lack of proper input validation and bounds checking represents a fundamental failure in secure coding practices that allows external data to influence internal program flow in unsafe ways.
Mitigation strategies must focus on both immediate patching and long-term defensive programming measures. The primary remediation is to upgrade the FLTK library to version 1.4.6 or later, where this integer overflow has been addressed by implementing proper checks for dimension validity before buffer allocation. Developers should ensure that all image dimensions are validated against maximum allowable limits defined by the BMP/ICO specifications and system memory constraints prior to any arithmetic operations involving those values. Additionally, incorporating static analysis tools configured to detect integer overflows in C++ codebases can help identify similar vulnerabilities early in the development lifecycle. Runtime protection mechanisms such as heap hardening features provided by modern operating systems, including Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP), should be enabled to mitigate the impact of any successful exploitation attempts by making it more difficult for attackers to predict memory layouts or execute injected code from corrupted heaps.