In builds of Open62541 that include PubSub and JSON support, a specially crafted JSON message triggers the decoder to write beyond a heap‑allocated array before any authentication check, resulting in a process crash and memory corruption.

The Open62541 library from o6 Automation GmbH is affected. Versions released prior to the stable 1.5.0 release are susceptible when PubSub and JSON features are enabled. The precise affected revision range is not published, but all builds before 1.5.0 with the mentioned modules are presumed vulnerable.

The CVSS score of 6.8 marks the issue as moderate, while the EPSS score of less than 1% indicates a low likelihood of exploitation in the wild. The vulnerability is not listed in the CISA KEV catalog. The likely attack vector is remote: an attacker can send a crafted JSON message over the network to a vulnerable Open62541 instance before authentication, which triggers the out‑of‑bounds write and causes a crash and memory corruption.