CVE-2025-26519 in libc
Summary
by MITRE • 02/14/2025
musl libc 0.9.13 through 1.2.5 before 1.2.6 has an out-of-bounds write vulnerability when an attacker can trigger iconv conversion of untrusted EUC-KR text to UTF-8.
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Analysis
by VulDB Data Team • 12/10/2025
The vulnerability identified as CVE-2025-26519 represents a critical out-of-bounds write flaw within the musl libc library version range 0.9.13 through 1.2.5, prior to the release of version 1.2.6. This issue specifically manifests during iconv conversion operations when processing untrusted EUC-KR text input destined for UTF-8 encoding. The vulnerability stems from inadequate bounds checking within the character encoding conversion routines, creating a potential avenue for arbitrary code execution or system compromise. The affected library serves as a fundamental component in numerous Linux distributions and embedded systems, amplifying the widespread impact of this flaw. This vulnerability falls under the CWE-787 Out-of-bounds Write classification, which is a well-documented weakness in software security that occurs when a program writes data past the end of a buffer or array. The flaw is particularly concerning because it can be triggered through user-controlled input during text processing operations, making it exploitable in various network-based and application contexts where character encoding conversion is performed.
The technical implementation of this vulnerability occurs within the iconv conversion functions of musl libc, specifically when handling EUC-KR encoded text that undergoes transformation to UTF-8 format. The flaw arises from improper validation of input character sequences and insufficient boundary checks during the conversion process. When an attacker supplies malformed EUC-KR input, the conversion routine fails to properly manage buffer boundaries, resulting in memory corruption that can be leveraged for privilege escalation or denial of service attacks. The vulnerability is particularly dangerous because it operates at the system library level, meaning that any application utilizing musl libc for text processing could potentially be exploited. This type of vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as exploitation could lead to arbitrary code execution, and T1499.004 for network denial of service through resource exhaustion attacks. The out-of-bounds write condition creates memory corruption that can be exploited to overwrite adjacent memory locations, potentially allowing attackers to manipulate program execution flow or inject malicious code.
The operational impact of CVE-2025-26519 extends across numerous computing environments that rely on musl libc for system operations, including embedded devices, containerized applications, and Linux-based systems where this lightweight C library is employed. Systems running affected versions of musl libc are vulnerable to remote exploitation when they process untrusted EUC-KR text input through iconv operations, making web applications, file processing utilities, and network services prime targets for exploitation. The vulnerability's exploitation potential increases significantly in environments where applications perform text conversion without proper input validation, particularly in internationalized applications that handle multiple character encodings. Organizations utilizing embedded systems, IoT devices, or containerized applications built on musl libc are particularly at risk, as these environments often lack the robust input validation mechanisms found in more complex operating systems. The widespread adoption of musl libc in Alpine Linux, Docker containers, and various embedded platforms means that this vulnerability affects a substantial portion of the Linux ecosystem, potentially creating cascading security implications across interconnected systems.
Mitigation strategies for CVE-2025-26519 primarily focus on upgrading to musl libc version 1.2.6 or later, which contains the necessary patches to address the out-of-bounds write vulnerability. System administrators should prioritize updating their environments, particularly those running embedded systems, containerized applications, or any infrastructure that relies on affected musl libc versions. Additionally, implementing input validation controls at application layers can provide defense-in-depth protection, ensuring that EUC-KR text inputs are properly sanitized before processing. Network segmentation and access controls should be enforced to limit potential exploitation vectors, particularly in environments where untrusted input processing occurs. Security monitoring should be enhanced to detect anomalous iconv operations or unusual text processing patterns that might indicate exploitation attempts. Organizations should also consider implementing runtime protections such as address space layout randomization and stack canaries to make exploitation more difficult. The vulnerability's classification as CWE-787 underscores the importance of rigorous buffer management practices and proper bounds checking in system libraries, which should be integrated into security development lifecycle processes. Regular vulnerability assessments and dependency monitoring are essential to prevent similar issues from arising in other system components that may be similarly vulnerable to out-of-bounds write conditions.