CVE-2026-21126 in Samsung
Summary
by MITRE • 10/12/2026
Improper input validation in getting cover image in libsimba.heifdec.media.samsung.so prior to SMR Oct-2026 Release 1 allows local attackers to write out-of-bounds memory.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified involves a critical failure in input validation within the HEIF decoding component of Samsung's proprietary library, specifically located at libsimba.heifdec.media.samsung.so. This flaw is present in software versions prior to the SMR October 2026 Release 1 update. The core issue stems from an improper handling of cover image data during the parsing and processing stages of High Efficiency Image File format files. When a maliciously crafted HEIF file containing malformed or excessively large metadata fields related to the cover image is processed, the application fails to adequately verify the boundaries of memory buffers allocated for storing this information. This lack of rigorous boundary checking allows an attacker to trigger a heap-based buffer overflow condition by writing data beyond the limits of the intended memory region.
From a technical perspective, this vulnerability aligns with Common Weakness Enumeration category CWE-120, which describes Buffer Copy without Checking Size of Input Classic Buffer Overflow, and more specifically CWE-787, Out-of-bounds Write. The absence of proper validation checks means that user-controlled input is directly used to determine memory write operations without ensuring the destination buffer has sufficient capacity. In modern mobile operating systems like Android, where this library operates, such out-of-bounds writes can corrupt adjacent heap metadata or overwrite critical function pointers and object structures stored in nearby memory locations. This corruption disrupts the normal execution flow of the application and creates an opportunity for arbitrary code execution if the attacker can precisely control the overwritten data to point to malicious shellcode placed elsewhere in the process address space.
The operational impact of this vulnerability is severe, particularly given its potential exploitation vector. Although classified as allowing local attackers to write out-of-bounds memory, on mobile platforms, a local attacker typically refers to another application installed on the same device or a compromised service with limited privileges. By exploiting this flaw, an adversary can escalate privileges from a low-privileged app context to that of the system media server or even gain root access if the affected library is invoked by higher-privilege processes during image processing tasks such as thumbnail generation or gallery preview rendering. This aligns with ATT&CK technique T1059, Command and Scripting Interpreter, specifically in the context of mobile exploitation where local privilege escalation leads to full device compromise. The ability to execute arbitrary code locally undermines the integrity and confidentiality of user data stored on the device.
Mitigation strategies primarily involve applying the vendor-provided security patch included in SMR October 2026 Release 1 or later, which addresses the input validation logic within the HEIF decoder. For organizations managing fleets of devices that cannot immediately update to the latest release, implementing strict application sandboxing and enforcing least-privilege principles can help contain potential damage from compromised applications. Additionally, deploying runtime memory protection mechanisms such as Address Space Layout Randomization (ASLR) and Heap Protection features like SafeHeap or Canary values can significantly increase the difficulty of successfully exploiting this vulnerability by making it harder for attackers to predict memory layouts and detect successful overwrites before code execution occurs. Regular security audits focusing on C/C++ buffer handling in native libraries are also recommended to prevent similar issues in future software updates.