The Linux kernel’s s390 pkey_pckmo handler fails to verify that the target buffer is large enough to hold the generated output from key_to_protkey(). When the handler produces data larger than the buffer, it writes past the end of the allocated memory, causing a kernel buffer overflow. This flaw is a classic out‑of‑bounds write (CWE‑787). The description does not specify privilege escalation or denial‑of‑service consequences beyond the overflow, but corruption of kernel memory could compromise system integrity.

The flaw affects Linux kernels built for the s390 architecture that implement the pkey_pckmo key handler. The provided data indicates all Linux kernels for that architecture are covered. Therefore any kernel variant that includes this code path may be vulnerable unless the kernel configuration disables the pkey feature.

The CVSS score of 7.8 indicates a high‑severity issue. The EPSS score is under 1%, suggesting a low probability of exploitation in the wild. The vulnerability is not listed in CISA’s KEV catalog. It is a local kernel flaw; an attacker would need the ability to execute code at kernel level or to manipulate the pkey interface to trigger the overflow. No known remote exploitation path is documented.