The vulnerability arises when a specially crafted input is provided to the fuzz_pkcs15_reader harness in OpenSC. The sc_pkcs15_pubkey_from_spki_fields() function allocates a zero-length buffer and then attempts to read one byte past the end of that allocation, resulting in an out-of-bounds heap read. This allows the caller to read data from an unintended memory location, potentially revealing sensitive information.

Affected systems are installations of OpenSC, the open source smart‑card tools and middleware, with any version released before 0.27.0. The issue was addressed and fixed in OpenSC 0.27.0; later releases are not affected.

The base CVSS score is 3.9, which indicates limited impact and complexity. EPSS data is unavailable, and the vulnerability is not listed in the CISA KEV catalog. Exploitation requires an attacker to supply a crafted input to the fuzz_pkcs15_reader harness; no mention is made of additional privileges or simultaneous conditions. The low score and lack of public exploitation evidence suggest a moderate risk in environments that expose the harness to untrusted input.