CVE-2026-109854 in Red Hat
Summary
by MITRE • 10/13/2026
A flaw was found in m17n-lib. An attacker who supplies crafted input to an application processing ISO-2022 encoded text can cause the library to read uninitialized memory from the stack. If the application exposes or returns the decoded output, this flaw can result in unexpected behavior and limited information disclosure.
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Analysis
by VulDB Data Team • 10/13/2026
The vulnerability identified within m17n-lib represents a critical class of software defects known as out-of-bounds reads resulting from improper initialization of local variables. This specific issue is triggered when an application processes text encoded using the ISO-2022 character encoding standard, a legacy multi-byte encoding scheme historically used for Japanese and other East Asian languages that relies on escape sequences to switch between different character sets. The core technical flaw lies in the library's handling of state transitions during the decoding process. When parsing these complex escape sequences, certain code paths fail to properly initialize stack-allocated buffers or variables before they are read. This lack of initialization means that if an attacker supplies crafted input designed to trigger this specific execution path, the application will access memory locations on the call stack that have not been explicitly set by the program logic.
From a technical perspective, this flaw aligns with CWE-457, which describes the use of uninitialized variables or pointers. In C and similar systems programming languages, local variables are allocated on the stack but do not automatically receive zeroed-out values unless explicitly initialized by the developer. When the m17n-lib library reads from these uninitialized memory locations to construct decoded output, it retrieves whatever data previously resided in that specific area of the stack. This behavior is particularly dangerous because modern operating systems and compilers often reuse stack frames for multiple function calls without clearing them entirely between invocations. Consequently, the content read by the vulnerable code may not be random garbage but rather sensitive information from previous operations performed by the same process or thread.
The operational impact of this vulnerability extends beyond simple application instability. While the immediate effect might manifest as unexpected behavior or crashes due to accessing invalid memory addresses, the more severe consequence is limited information disclosure. If the application that utilizes m17n-lib exposes or returns the decoded output directly to an attacker, such as through a web response header, API endpoint, or error message, it can inadvertently leak sensitive data from the stack. This could include authentication tokens, session identifiers, private keys, passwords, or other proprietary information stored in memory by prior function calls within the same process context. Such leaks facilitate further attacks, including privilege escalation or unauthorized access to protected resources, thereby compromising the confidentiality and integrity of the affected system.
This vulnerability is categorized under MITRE ATT&CK technique T1083, which covers File and Directory Discovery, although in this specific instance, it serves as a mechanism for information gathering rather than direct file system interaction. More broadly, it falls under the broader category of Memory Corruption vulnerabilities often associated with CWE-200, where an attacker gains access to sensitive information that was not intended to be disclosed. The risk is exacerbated by the fact that ISO-2022 encoding involves complex state machines and escape sequences that are less commonly tested in modern development environments compared to UTF-8, leading to potential gaps in input validation and boundary checking logic within legacy libraries like m17n-lib.
To mitigate this vulnerability, developers must ensure that all local variables used for storing decoded data or intermediate processing states are explicitly initialized before being read or returned. This can be achieved by using compiler flags such as -Wuninitialized to detect potential uses of uninitialized values during the build process and addressing any warnings raised. Additionally, implementing strict input validation on incoming ISO-2022 encoded streams is essential to prevent malformed escape sequences from triggering undefined behavior. For applications relying on m17n-lib, updating to a patched version that addresses this specific initialization flaw is critical. In environments where immediate patching is not feasible, deploying runtime protection mechanisms such as Address Sanitizer (ASan) during testing or utilizing memory-safe wrappers can help detect and prevent the exploitation of uninitialized memory reads before they reach production systems.