Security Bulletin
Summary
At several points during QPY format deserialization for QPY format versions >=13 there was unbound recursion in the processing of the payloads. A maliciously crafted QPY payload could use this to cause the deserialization to exceed the stack limit and cause a segmentation fault from a stack overflow.
Vulnerability Details
CVEID: CVE-2026-116500
DESCRIPTION: Qiskit SDK could allow a local attacker to cause a denial of service due to unbound recursion during deserialization of untrusted QPY payloads.
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 | v2.4.0-v2.6.1 |
Remediation/Fixes
Remediation/Fixes guidance:
The issue is addressed in Qiskit versions v2.6.2.
| Product(s) | Version(s) number and/or range | Remediation/Fix/Instructions |
| <Qiskit SDK - qiskit.qpy.load() function> | v2.6.2 |
Upgrade to the patched versions: qiskit v2.6.2. |
Workarounds and Mitigations
Workarounds/Mitigation guidance:
None
Get Notified about Future Security Bulletins
References
Reference guidance:
1. IBM strongly recommends upgrading Qiskit to v2.6.2
Acknowledgement
The vulnerability was reported to IBM by Nathan Rebello.
Change History
05 Nov 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:
05 November 2026
Initial Publish date:
05 November 2026
UID
ibm17295235