CVE-2026-111137: Out-of-bounds Write in amartin755 libsmi

CVE-2026-111137 is an out-of-bounds write vulnerability in libsmi through version 0.5.0, specifically in the smiValueAsString() function located in lib/smi.c. The vulnerability arises from improper handling of OCTET STRING values during hex rendering, where a fixed 1024-byte static buffer can be overflowed. An attacker can exploit this by providing a malicious MIB containing an OCTET STRING DEFVAL of 512 or more octets with a leading 0x00 byte, leading to corruption of adjacent library globals and potential crash of applications like smidump that consume libsmi.

Successful exploitation can cause memory corruption by overflowing a static buffer, leading to application crashes (denial of service) in smidump or other programs using libsmi. There is no indication of code execution or privilege escalation. The CVSS 4.0 score is 6.9 (medium severity), reflecting local attack vector with low complexity and no privileges required but requiring user interaction.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, avoid processing untrusted or crafted MIB files containing large OCTET STRING DEFVALs with leading 0x00 bytes. Monitor vendor communications for official patches or updates addressing this vulnerability.