Security Bulletin
Summary
A maliciously constructed QPY payload that contains specifically constructed ParameterExpression objects as part of the payload can trigger a segfault in the evaluation of those expressions during deserialization. The function qiskit.qpy.load() may recurse too deeply and overflow the available stack space, when deserializing these QPY payloads.
Vulnerability Details
CVEID: CVE-2026-19795
DESCRIPTION: Qiskit could allow a local attacker to cause a denial of service due to improper handling of a specially crafted object during deserialization. A malicious QPY payload can trigger a segmentation fault, causing the application to crash when deserializing untrusted input.
CWE: CWE-502: Deserialization of Untrusted Data
CVSS Source: IBM
CVSS Base score: 6.2
CVSS Vector: (CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
Affected Products and Versions
| Affected Product(s) | Version(s) |
| Qiskit SDK | 2.1.0 - 2.5.1 |
Remediation/Fixes
Remediation/Fixes guidance:
The issue is addressed in Qiskit versions v2.5.2. This version is patched to prevent the stack overflow by no longer evaluating the expression tree for ParameterExpression objects recursively.
| Product(s) | Version(s) number and/or range | Remediation/Fix/Instructions |
| <Qiskit SDK - qiskit.qpy.load() function> | v2.5.2 |
Upgrade to the patched versions: qiskit v2.5.2. |
Workarounds and Mitigations
Workarounds/Mitigation guidance:
None
Get Notified about Future Security Bulletins
References
Reference guidance:
1. IBM strongly recommends upgrading Qiskit to v2.5.2
Acknowledgement
Issue discovered by Matthew Treinish (IBM) and Takashi Imamichi (IBM)
Change History
03 Sep 2026: Initial Publication
*The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin.
Disclaimer
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Document Location
Worldwide
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Document Information
Modified date:
03 September 2026
Initial Publish date:
03 September 2026
UID
ibm17285932