CVE-2026-111137 in libsmi
Summary
by MITRE • 10/15/2026
libsmi through 0.5.0 contains an out-of-bounds write vulnerability in smiValueAsString() in lib/smi.c that allows attackers to overflow a fixed 1024-byte static buffer through hex rendering of OCTET STRING values. Attackers can supply a crafted MIB with an OCTET STRING DEFVAL of 512 or more octets and a leading 0x00 byte to corrupt adjacent library globals and crash smidump or other consumers.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in libsmi versions through 0.5.0 represents a critical memory safety flaw located within the smiValueAsString function found in the lib/smi.c source file. This specific implementation defect is classified as an out-of-bounds write, which falls under the Common Weakness Enumeration category CWE-787: Out-of-Bounds Write. The core of the issue lies in how the library handles the conversion of Simple Network Management Protocol (SNMP) Object Identifier values into their string representations. Specifically, when processing OCTET STRING data types, the function utilizes a fixed-size static buffer with a capacity of 1024 bytes to store the resulting hexadecimal representation of the value. The flaw arises because the code fails to adequately validate the length of the input OCTET STRING against this hardcoded limit before performing the write operation. Consequently, if an attacker provides a crafted Management Information Base (MIB) file containing an OCTET STRING definition with a DEFVAL attribute consisting of 512 or more octets, and crucially includes a leading zero byte to trigger specific hex rendering logic, the resulting hexadecimal string can exceed the buffer's capacity. This mismatch between the expected input size and the fixed output buffer allocation leads directly to memory corruption as data is written beyond the allocated boundaries into adjacent memory regions.
The operational impact of this vulnerability extends far beyond simple application instability. Because the overflow targets a static buffer within the library itself, the corrupted data does not merely affect local stack variables but can overwrite global state and other critical structures residing in adjacent memory locations. This capability allows an attacker to achieve arbitrary code execution or cause a denial of service by crashing processes that consume libsmi, such as smidump or various network monitoring tools. The ability to corrupt library globals is particularly severe because it undermines the integrity of the entire application environment rather than just isolating the fault within a single function call. From an offensive security perspective, this vulnerability aligns with ATT&CK technique T1059: Command and Scripting Interpreter if exploited for code execution, or more broadly fits into lateral movement scenarios where compromised network management tools are leveraged to gain deeper access to infrastructure. The specific vector of supplying a crafted MIB file suggests that the attack surface is primarily associated with systems that parse untrusted or semi-trusted SNMP definitions, making devices and servers involved in network administration high-risk targets.
Mitigation strategies for this vulnerability require both immediate patching and long-term architectural improvements. The most effective remediation is to upgrade libsmi to a version later than 0.5.0 where the out-of-bounds write has been addressed by implementing proper bounds checking before writing to the static buffer. Developers must ensure that any function handling variable-length input data, particularly those converting binary structures like OCTET STRINGs into text formats, performs rigorous length validation against the destination buffer size. In addition to patching, organizations should enforce strict input sanitization policies for all MIB files processed by their network management systems. This includes validating the structure and content of incoming SNMP definitions before they are passed to parsing libraries. Furthermore, adopting memory-safe programming practices or utilizing static analysis tools during development can help detect similar buffer overflow risks early in the software lifecycle. For environments where upgrading is not immediately feasible, deploying runtime application self-protection mechanisms or network intrusion detection systems that monitor for anomalous behavior from smidump and related processes may provide a layer of defense against exploitation attempts targeting this specific memory corruption flaw.