CVE-2026-4870 Overview
CVE-2026-4870 is a denial of service vulnerability in the IBM Qiskit Software Development Kit (SDK). The flaw affects versions 0.43.0 through 2.5.0 of the quantum computing framework. An attacker can trigger uncontrolled recursion in the parser, resulting in a segmentation fault that crashes the process. The vulnerability is classified under CWE-674: Uncontrolled Recursion and is exploitable over the network without authentication or user interaction. IBM has published advisory information on the IBM Support Page.
Critical Impact
Remote unauthenticated attackers can crash applications using vulnerable Qiskit SDK versions by submitting crafted input that triggers parser recursion and a segmentation fault.
Affected Products
- IBM Qiskit Software Development Kit 0.43.0
- IBM Qiskit Software Development Kit versions through 2.5.0
- Applications and services embedding vulnerable Qiskit SDK releases
Discovery Timeline
- 2026-06-12 - CVE-2026-4870 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2026-4870
Vulnerability Analysis
The IBM Qiskit SDK contains a parser component that processes structured input without enforcing a recursion depth limit. When an attacker submits crafted input containing deeply nested constructs, the parser recurses repeatedly. Each recursive call consumes stack space until the process exhausts its available stack and receives a segmentation fault from the operating system. The crash terminates the host process and any quantum workflows depending on it. Because the vulnerability resides in input parsing, exposure depends on whether the application accepts Qiskit-parsed content from untrusted sources.
Root Cause
The root cause is the absence of recursion depth enforcement in the parser logic. The parser implementation in versions 0.43.0 through 2.5.0 recurses on nested input without a guard clause. This pattern matches CWE-674: Uncontrolled Recursion. Stack-based recursion in interpreted and native code paths can exhaust process memory before any application-level error handling executes.
Attack Vector
An attacker delivers malformed or maliciously nested input to a service or application that invokes the Qiskit parser. No credentials or user interaction are required. Network-accessible services that accept Qiskit circuit definitions, OpenQASM strings, or related serialized formats from untrusted clients are the primary exposure. The result is a process crash and loss of availability for the affected workload. The vulnerability does not affect confidentiality or integrity.
No public proof-of-concept is available at the time of publication. Review the IBM Support Page for parser input formats covered by the advisory.
Detection Methods for CVE-2026-4870
Indicators of Compromise
- Unexpected SIGSEGV (signal 11) terminations in processes that import the qiskit Python package.
- Repeated crash-restart cycles in services that expose Qiskit parsing endpoints to network clients.
- Application logs showing parser invocations immediately preceding abrupt process exit without a Python traceback.
Detection Strategies
- Inventory Python environments and identify installations of qiskit between versions 0.43.0 and 2.5.0 using pip show qiskit or software composition analysis tooling.
- Monitor application telemetry for segmentation faults and core dumps correlated with Qiskit parser entry points.
- Inspect inbound payloads to Qiskit-enabled services for abnormally deep nesting structures.
Monitoring Recommendations
- Forward process crash events and core dump metadata to a centralized logging platform for correlation.
- Alert on sudden increases in restart counts for containerized workloads that include Qiskit dependencies.
- Track network requests targeting Qiskit API endpoints and baseline payload size and structure depth.
How to Mitigate CVE-2026-4870
Immediate Actions Required
- Upgrade IBM Qiskit SDK to a version later than 2.5.0 as directed by the IBM Support Page.
- Restrict network access to services that expose Qiskit parsing functionality to trusted clients only.
- Validate and reject input payloads containing excessive nesting depth before invoking the Qiskit parser.
Patch Information
IBM has published remediation guidance on the IBM Support Page. Apply the fixed Qiskit SDK release identified in that advisory to all development, build, and production environments. Rebuild and redeploy container images and Python virtual environments that bundle Qiskit after upgrading the package.
Workarounds
- Place vulnerable services behind a reverse proxy that enforces request size and structural complexity limits.
- Run Qiskit-dependent workloads with process supervisors that restart on crash to maintain availability while patches are deployed.
- Sandbox Qiskit parsing in isolated worker processes so that a segmentation fault does not affect the parent service.
# Configuration example
pip install --upgrade qiskit
pip show qiskit | grep -i version
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
