The flaw is an out-of-bound read performed by the client-side function responseReadNamespacesArray() in open62541 1.5.5. When a server sends a malformed namespace array, the client attempts to read beyond the bounds of its buffer, which can cause the client process to terminate unexpectedly. The only documented effect is denial of service.

Applications compiled with open62541 version 1.5.5 that process namespace array responses are affected. Since no specific vendors are listed, any distribution of this release is vulnerable until a patch is applied.

The CVSS score of 7.5 classifies the flaw as high severity. The EPSS score is less than 1%, indicating a low probability of exploitation in the near term. The vulnerability is not listed in the CISA KEV catalog. An attacker who can control the server that a vulnerable client connects to could craft a malicious response to trigger the out-of-bounds read, leading to a crash. This attack vector is inferred from the nature of the vulnerability, and no public exploitation has been reported.