# CVE-2026-4870: IBM Qiskit SDK denial of service via uncontrolled recursion in parser

Source: https://junglewise.ai/threats/cve-2026-4870-ibm-qiskit-sdk-denial-of-service-via-uncontrolled-recursion-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-12. Updated: 2026-06-12  
License: CC BY 4.0 with a link back

CVE-2026-4870 · Severity: high · CVSS 7.5 · Published 2026-06-12

IBM Qiskit SDK, a software development kit for quantum computing, is vulnerable to a flaw that can cause applications to crash. By providing specially crafted quantum circuit descriptions (OpenQASM), an attacker can trigger a memory error that shuts down the service. This results in a denial of service, preventing researchers or automated systems from processing quantum programs.

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

## Quick answers

**Is CVE-2026-4870 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-4870 being exploited in the wild.

**How severe is CVE-2026-4870?** High severity, with a CVSS score of 7.5, published 12 June 2026.

**Which products and versions are affected?** IBM Qiskit SDK 0.43.0 - 2.5.0.

**Is there a fix for CVE-2026-4870?** A patch was published on 2026-06-12. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-4870 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-4870?** 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

A vulnerability in the OpenQASM 2 parser of the IBM Qiskit SDK (specifically within qiskit.qasm2.load, qiskit.qasm2.loads, and QuantumCircuit.from_qasm_str) allows for uncontrolled recursion. When the parser encounters deeply nested classical expressions, it can overflow the available stack space, resulting in a segmentation fault. This is a remote attack vector if the application processes user-supplied QASM strings or files without prior validation. The issue is mitigated in patched versions by enforcing the Python recursion limit and raising a standard RecursionError instead of crashing the process. Patches are available in versions 1.4.6 and 2.4.2.

## Affected products

- IBM Qiskit SDK 0.43.0 - 2.5.0

## Timeline

- 2026-06-12: disclosed
- 2026-06-12: advisory
- 2026-06-12: patched

## References

- [https://www.ibm.com/support/pages/node/7276123](https://www.ibm.com/support/pages/node/7276123)

## Related threats

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- [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)
- [Qiskit SDK stack overflow in QPY deserialization](https://junglewise.ai/threats/cve-2026-19795-qiskit-sdk-stack-overflow-in-qpy-deserialization)