CVE-2026-96611 in FFmpeg
Summary
by MITRE • 09/23/2026
FFmpeg before 9.0 has a signed integer overflow in libavformat/mov.c. In mov_read_ispe(), uint32_t width/height values from a crafted HEIF ispe box are stored into signed int fields without bounds checking, allowing values exceeding INT_MAX to become negative. In read_image_grid(), accumulating these values causes signed integer overflow (undefined behavior per C17 section 6.5), which on x86 wraps to a small positive value, bypassing downstream validity checks.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified in FFmpeg versions prior to 9.0 represents a critical security flaw rooted in improper handling of signed integer arithmetic within the libavformat library, specifically affecting the processing of HEIF image files. The core issue resides in the mov_read_ispe function, which is responsible for parsing the Image Spatial Extent box from MOV and related container formats that support HEIF content. During this process, width and height values extracted from the crafted input file are stored into signed integer fields without performing adequate bounds checking or validation against maximum allowable limits. This design oversight allows an attacker to supply uint32_t values that exceed INT_MAX, causing these positive integers to be interpreted as negative numbers due to sign extension errors inherent in the type conversion process.
This initial misinterpretation of data types sets off a chain reaction leading to undefined behavior within the C17 standard framework. Specifically, when read_image_grid attempts to accumulate these incorrectly signed values for further processing or memory allocation calculations, it triggers a signed integer overflow. According to section 6.5 of the C17 specification, signed integer overflow constitutes undefined behavior, meaning the compiler and runtime environment are not required to handle this scenario predictably. However, on x86 architectures utilizing two's complement arithmetic, which is prevalent in most modern computing environments, this overflow typically wraps around to a small positive value rather than causing an immediate crash or exception. This wrapping effect effectively masks the error from basic sanity checks that might otherwise detect invalid dimensions.
The operational impact of this vulnerability is severe because it allows maliciously crafted HEIF files to bypass downstream validity checks designed to prevent buffer overflows and out-of-bounds memory accesses. By manipulating width and height values into negative numbers that wrap around during arithmetic operations, an attacker can trick the decoder into allocating insufficient buffers or accessing invalid memory regions. This discrepancy between expected and actual memory layout creates opportunities for arbitrary code execution if the subsequent processing steps rely on these corrupted dimensions to determine buffer sizes or array indices. The flaw essentially undermines the integrity of the media parsing pipeline, turning a standard image decoding routine into a potential attack vector for remote exploitation.
From a classification perspective, this vulnerability aligns with CWE-190, which describes integer overflow or wraparound issues that can lead to other vulnerabilities such as buffer overflows. It also relates closely to CWE-682 regarding incorrect calculation of size and quantity, where the failure to properly validate input ranges leads to erroneous resource allocation decisions. In terms of offensive security frameworks like MITRE ATT&CK, this technique falls under T1059 Command and Scripting Interpreter or potentially T1203 Exploitation for Client Execution if leveraged through a compromised media player application that utilizes FFmpeg as its backend engine. The attack vector typically involves tricking a user into opening a specially crafted HEIF file within an affected version of FFmpeg-based software, such as video players, image viewers, or web browsers with integrated media support.
Mitigation strategies must focus on immediate patching and defensive coding practices. Users should upgrade to FFmpeg version 9.0 or later where this issue has been addressed through stricter input validation and proper use of unsigned integer types for dimensions that are inherently non-negative. Developers integrating FFmpeg into their applications should ensure they are using the latest stable releases and consider implementing additional sanity checks at the application layer before passing data to the library. Furthermore, adopting static analysis tools capable of detecting signed-unsigned conversion issues can help identify similar vulnerabilities in custom codebases. Security teams should also monitor for new CVEs related to FFmpeg's media parsing components and apply updates promptly to maintain a secure posture against exploitation attempts targeting multimedia processing libraries.