# CVE-2026-19795: Qiskit SDK stack overflow in QPY deserialization

Source: https://junglewise.ai/threats/cve-2026-19795-qiskit-sdk-stack-overflow-in-qpy-deserialization  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-03. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-19795 · Severity: medium · CVSS 6.2 · Published 2026-09-03

Qiskit SDK is a quantum computing library used by researchers and developers to design and simulate quantum circuits. A flaw in how the library processes QPY (Qiskit Pickle YAML) files allows an attacker to craft a malicious file that causes the application to crash when loaded, disrupting work and potentially impacting dependent systems or services.

Technologies: [IBM Qiskit SDK](https://junglewise.ai/threats/technologies/qiskit-sdk). Vendors: [IBM](https://junglewise.ai/threats/vendors/ibm).

## Quick answers

**Is CVE-2026-19795 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-19795 being exploited in the wild.

**How severe is CVE-2026-19795?** Medium severity, with a CVSS score of 6.2, published 3 September 2026.

**Which products and versions are affected?** IBM Qiskit SDK 2.1.0 through 2.5.1.

**Is there a fix for CVE-2026-19795?** A patch was published on 2026-09-03: Fixed in Qiskit v2.5.2 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-19795 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-19795?** Check whether you run IBM Qiskit SDK at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in the deserialization logic of qiskit.qpy.load(), which recursively evaluates ParameterExpression objects in QPY payloads without proper depth limits. An attacker can craft a specially constructed QPY file with deeply nested ParameterExpression objects that triggers excessive recursion, overflowing the stack and causing a segmentation fault. The attack requires local file access or the ability to supply untrusted QPY input to the application; no authentication or user interaction is required once the malicious file is processed. The impact is denial of service through application crash. IBM patched this in Qiskit v2.5.2 by eliminating the recursive evaluation of the expression tree; versions 2.1.0 through 2.5.1 are affected.

## Affected products

- IBM Qiskit SDK 2.1.0 through 2.5.1

## Timeline

- 2026-09-03: disclosed
- 2026-09-03: patched: Fixed in Qiskit v2.5.2

## References

- [https://www.ibm.com/support/pages/node/7285932](https://www.ibm.com/support/pages/node/7285932)

## Related threats

- [IBM Qiskit SDK out-of-bounds write in unitary matrix handler](https://junglewise.ai/threats/cve-2026-116501-ibm-qiskit-sdk-2-4-0-through-2-6-1-could-allow-a-local-attacker)
- [IBM Qiskit SDK unbound recursion in QPY deserialization](https://junglewise.ai/threats/cve-2026-116500-ibm-qiskit-sdk-2-4-0-through-2-6-1-could-allow-a-local-attacker)
- [IBM Qiskit SDK unsafe deserialization in QPY format](https://junglewise.ai/threats/cve-2026-116499-ibm-qiskit-sdk-1-4-2-through-2-6-2-could-allow-a-local-attacker)
- [IBM Qiskit SDK denial of service via uncontrolled recursion in parser](https://junglewise.ai/threats/cve-2026-4870-ibm-qiskit-sdk-denial-of-service-via-uncontrolled-recursion-in)