CVE-2026-21111 in One UI
Summary
by MITRE • 09/09/2026
Out-of-bounds write in libsthmbc.so prior to One UI 8.5 allows local attackers to write out-of-bounds memory.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified as an out-of-bounds write within the libsthmbc.so library, present in Samsung devices running software versions prior to One UI 8.5, represents a critical memory safety failure that compromises the integrity of the operating system's execution environment. This specific dynamic shared object is typically associated with hardware abstraction layers or security-related subsystems on Android-based mobile platforms, often handling secure element communications or biometric processing functions. The root cause lies in improper validation of input parameters passed to internal buffer management routines within this library. When a local attacker triggers the vulnerable code path by supplying crafted data that exceeds the allocated memory boundaries for a specific buffer, the application writes data beyond the end of the intended array or heap allocation. This type of flaw is formally categorized under CWE-787: Out-of-bounds Write in standard vulnerability classification systems, indicating a failure to enforce strict bounds checking on memory access operations.
From an operational perspective, out-of-bounds write vulnerabilities are particularly dangerous because they allow attackers to corrupt adjacent memory structures rather than just reading sensitive information as seen in buffer over-reads. By carefully crafting the payload, a local attacker can overwrite critical metadata such as heap headers, function pointers, or return addresses stored on the stack. This corruption enables arbitrary code execution with the privileges of the compromised process. In the context of mobile operating systems like Android, if libsthmbc.so operates within a privileged daemon or has elevated permissions due to its role in handling secure hardware interactions, successful exploitation could lead to full system compromise. The attacker gains the ability to inject malicious logic into the target process memory space, potentially bypassing sandbox restrictions and gaining control over sensitive subsystems including biometric authentication modules or secure element interfaces.
The attack vector for this vulnerability is classified as local, meaning that an adversary must first have access to the device, either through physical possession or by having already compromised a lower-privilege application on the same system. This aligns with ATT&CK technique T1059: Command and Scripting Interpreter if used in conjunction with other exploits, but more specifically relates to memory corruption techniques often leveraged during privilege escalation phases of an attack chain. Local attackers can exploit this flaw to escalate privileges from a restricted app context to higher-level system services or the kernel itself, depending on how the library is integrated into the broader Android security architecture. The impact extends beyond simple data theft; it undermines the fundamental trust model of the device by allowing unauthorized modification of executable code and control flow mechanisms that are designed to remain immutable during normal operation.
Mitigation strategies for this vulnerability primarily involve software updates provided by the vendor, which include patches implementing rigorous bounds checking and memory safety improvements within libsthmbc.so. Organizations managing fleets of these devices should prioritize applying security patches associated with One UI 8.5 or later releases immediately upon availability to close the window of exposure. For environments where immediate patching is not feasible, defense-in-depth measures such as enforcing strict application sandboxing policies and disabling unnecessary permissions for applications that might interact with biometric or secure element services can reduce the attack surface. Additionally, enabling hardware-backed security features like Samsung Knox Attestation helps ensure that even if memory corruption occurs, subsequent attempts to establish persistent access or tamper with system integrity are detected and blocked by root detection mechanisms. Continuous monitoring of application behavior for anomalous memory access patterns using runtime application self-protection tools can also provide an additional layer of defense against exploitation attempts targeting this class of vulnerabilities.