CVE-2026-107167 in m17n-lib
Summary
by MITRE • 10/07/2026
A flaw was found in m17n-lib. A user providing specially crafted text input can trigger a heap use-after-free condition during input-method state transitions. Under specific conditions, the library frees an internal input context object but subsequently attempts to write to that freed memory. This issue can cause applications relying on the library to crash, leading to a Denial of Service (DoS), or potentially allow arbitrary code execution.
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Analysis
by VulDB Data Team • 10/07/2026
The vulnerability identified in m17n-lib represents a critical heap-based use-after-free condition arising from improper management of internal input context objects during state transitions within its internationalization and input method processing subsystems. This library, which serves as a foundational component for handling multilingual text entry across various operating systems and applications, failed to maintain proper reference counting or memory safety guarantees when transitioning between different input states. Specifically, the flaw allows an attacker who can provide specially crafted text input to trigger a scenario where the application frees an internal context object but subsequently attempts to write data to that already deallocated memory region. This sequence of events indicates a fundamental lapse in pointer lifecycle management, where the library does not adequately nullify pointers or check for validity before performing subsequent operations on freed resources.
From a technical perspective, this defect aligns with CWE-416, Use After Free, which is categorized as a high-severity memory corruption vulnerability. The core issue lies in the asynchronous nature of input method state changes combined with aggressive memory optimization that does not account for all execution paths leading to context destruction. When an application processes complex or malformed Unicode sequences designed to exploit this race condition or logical error, it forces the library into a state where the internal pointer remains valid from the perspective of subsequent code blocks but points to invalid heap memory managed by the system allocator. This discrepancy allows for out-of-bounds writes that can corrupt adjacent heap metadata or overwrite critical data structures within the process address space.
The operational impact of this vulnerability is twofold, encompassing both reliability and security implications. In its most immediate manifestation, the use-after-free condition leads to application crashes, resulting in a Denial of Service for users relying on m17n-lib for text input. This disrupts productivity and system stability, particularly in environments where continuous text processing is required. However, the more severe implication involves potential arbitrary code execution. By carefully crafting heap layouts through repeated exploitation attempts, an attacker can manipulate the freed memory to contain malicious payloads or control flow gadgets. When the library writes to this corrupted location, it may overwrite function pointers or return addresses, thereby hijacking the execution flow of the host application. This capability transforms a simple stability issue into a critical remote code execution vector if the vulnerable application processes untrusted input from external sources.
In terms of threat modeling and industry standards, this vulnerability maps closely to MITRE ATT&CK technique T1203, Exploitation for Client Execution, particularly in scenarios where an attacker lures a user into opening a document or interacting with a UI element that triggers the vulnerable code path. It also relates to CWE-787, Out-of-bounds Write, as the write operation occurs on memory outside its intended allocation boundaries due to the use of stale pointers. The attack vector is typically classified as Local if it requires user interaction within an application using m17n-lib, but could be Remote if integrated into network-facing services that process text input without adequate sanitization or sandboxing.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. Developers should prioritize updating to patched versions of m17n-lib where the internal reference counting mechanisms have been corrected to ensure context objects are not freed while still in use during state transitions. For applications unable to update immediately, implementing strict input validation and sanitization can reduce the attack surface by filtering out malformed Unicode sequences that trigger the specific state transition logic exploited by this flaw. Additionally, enabling memory protection features such as Address Space Layout Randomization (ASLR) and Heap Canaries can significantly raise the difficulty of successful exploitation by randomizing memory layouts and detecting corruption before it leads to code execution. Long-term solutions involve adopting safer programming practices or libraries that enforce strict ownership semantics for dynamic resources, thereby eliminating entire classes of use-after-free vulnerabilities at their source.