CVE-2026-120208 in libheif
Summary
by MITRE • 10/31/2026
libheif 1.18.0 before 1.23.3 contains a heap-based buffer overflow vulnerability in unc_decoder_mixed_interleave::processTile() that allows attackers to write out of bounds by supplying chroma components with unequal bit depths. Attackers can craft a HEIF file declaring, for example, 16-bit Cb and 8-bit Cr to trigger file-controlled heap writes past the Cr plane, potentially achieving code execution in image-processing pipelines.
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Analysis
by VulDB Data Team • 10/31/2026
The vulnerability identified in libheif versions prior to 1.23.3 represents a critical security flaw within the HEIF (High Efficiency Image File Format) decoding pipeline, specifically located in the unc_decoder_mixed_interleave::processTile() function. This heap-based buffer overflow arises from an insufficient validation of chroma component bit depths during the image processing phase. The HEIF standard allows for various color space configurations, including those where the luminance and chroma components may have different sample resolutions or bit depths. However, in this specific implementation, the decoder fails to correctly calculate memory allocation sizes or bounds when handling mixed interleave modes with unequal chroma bit depths, such as a scenario involving 16-bit Cb (blue-difference) and 8-bit Cr (red-difference) components. This discrepancy leads to miscalculations in buffer sizing, creating an opportunity for out-of-bounds memory writes that extend beyond the allocated heap space designated for the Cr plane.
From a technical perspective, this flaw is classified under CWE-122: Heap-based Buffer Overflow, which occurs when data written to a heap-allocated buffer exceeds its boundaries, potentially overwriting adjacent metadata or executable code structures on the heap. The attack vector relies on an adversary crafting a malicious HEIF file that explicitly declares these unequal chroma bit depths in its header and payload structure. When a victim application utilizing libheif processes this crafted image, the decoder attempts to process the tile data without properly accounting for the larger size required by the 16-bit Cb component relative to the allocated space for the 8-bit Cr component. Consequently, write operations intended for the chroma plane spill over into adjacent memory regions. This out-of-bounds access can corrupt heap metadata or overwrite function pointers and return addresses stored in nearby allocations, which is a classic precursor to arbitrary code execution.
The operational impact of this vulnerability is severe, particularly given libheif's widespread adoption as a core library for image processing across various operating systems, web browsers, mobile applications, and content management systems. If an attacker can trick a user into opening or automatically processing the malicious HEIF file within an application that integrates libheif, they may achieve remote code execution with the privileges of the target process. This capability allows attackers to install malware, exfiltrate sensitive data, establish persistence mechanisms, or pivot further into internal networks depending on the context in which the image is processed. The risk is amplified by the fact that many applications automatically decode images upon upload or display without rigorous sandboxing, making this a potent vector for drive-by attacks and supply chain compromises where malicious images are embedded in larger datasets.
In terms of threat modeling, this vulnerability aligns with MITRE ATT&CK technique T1203: Exploitation for Client Execution, as it targets client-side software to execute arbitrary code through the exploitation of a specific application feature (image decoding). It also relates to CWE-787: Out-of-bounds Write in terms of memory corruption mechanics. To mitigate this risk, organizations and developers must immediately update libheif to version 1.23.3 or later, where the issue has been resolved by implementing stricter validation checks for chroma bit depth consistency and ensuring that buffer allocations accurately reflect the maximum required size based on all component specifications. Additionally, defensive measures should include deploying input sanitization layers at network boundaries to inspect incoming image files for anomalous metadata structures before they reach vulnerable libraries. For applications where libheif is embedded, enabling sandboxing or using restricted execution environments can limit the blast radius of a successful exploitation attempt, while regular security audits and fuzz testing of image parsing routines are recommended to detect similar logic errors in other codecs.