CVE-2026-56786 is an out-of-bounds write vulnerability in tomojitakasu RTKLIB through version 2.4.3. The issue exists in the decode_type1033 function, which fails to properly clamp length counters to the size of the destination buffer, resulting in an overflow of up to 191 bytes into adjacent fixed 64-byte descriptor fields. An attacker who can control an NTRIP or serial RTCM3 correction stream can send a specially crafted CRC-valid type-1033 message to corrupt adjacent members of the rtcm_t object. This memory corruption can lead to arbitrary code execution or denial of service conditions. The vulnerability is remotely exploitable without authentication and requires no user interaction, making it highly critical. No vendor advisory or patch information is currently available.

Successful exploitation allows remote attackers to corrupt memory adjacent to a fixed-size buffer in RTKLIB, potentially enabling arbitrary code execution or causing denial of service. The vulnerability affects systems processing NTRIP or serial RTCM3 correction streams with vulnerable RTKLIB versions. The high CVSS score (9.3) reflects the critical nature of this remote, unauthenticated, high-impact vulnerability.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, users should consider restricting or validating input from NTRIP or serial RTCM3 correction streams to untrusted sources to reduce exposure. Monitor vendor channels for updates and apply patches promptly once released.