IBM Qiskit SDK versions 2.1.0 through 2.5.1 handle the deserialization of QPY files insecurely. A crafted QPY payload can trigger a segmentation fault by overflowing the stack or improperly evaluating the expression tree for ParameterExpression objects. This results in the application crashing, effectively denying service to legitimate users. The weakness is a classic example of deserialization of untrusted data, identified as CWE‑502.

The vulnerability affects IBM Qiskit SDK, specifically versions 2.1.0 up to 2.5.1 inclusive. The patch is included in version 2.5.2 and later, which disables the recursive evaluation of the expression tree during deserialization.

The CVSS score of 6.2 indicates moderate severity, and the EPSS score is currently unavailable, so exploitation probability cannot be precisely quantified. The vulnerability is listed as not in CISA’s KEV catalog. Based on the description, the attack vector is likely local: an attacker must supply a malicious QPY file to the application, a condition that can be mitigated by removing or restricting untrusted QPY input. No workaround is available, so a direct code update is required.