Cyber Resilience

CVE-2026-104020

DoS

Published
01 October 2026
Modified
02 October 2026
CVSS Score v4 8.7
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0044 36th percentile
Risk Priority 44 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-104020 is a high-severity Uncontrolled Recursion (CWE-674) vulnerability in Amazon Ion Python (inferred from references). Its CVSS base score is 8.7 (High).

Operationally, ranked at the 36th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) and SI-4 (System Monitoring) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

Uncontrolled recursion in the Ion reader in Amazon Ion Python before 0.15.0 might allow a remote unauthenticated actor to crash the application using the library, resulting in a denial of service, via a crafted, deeply nested Ion value. To remediate…

more

this issue, users should upgrade to version 0.15.0 or later.

CWE(s)

Related Threats

CVEs Like This One

CVE-2026-102495Shared CWE-674
CVE-2024-34158Shared CWE-674
CVE-2025-7010Shared CWE-674
CVE-2026-95844Shared CWE-674
CVE-2026-77465Shared CWE-674
CVE-2024-0210Shared CWE-674
CVE-2024-20311Shared CWE-674
CVE-2023-52761Shared CWE-674
CVE-2026-40345Shared CWE-674
CVE-2026-6479Shared CWE-674

Affected Assets

Amazon
Ion Python
inferred from references and description; NVD did not file a CPE for this CVE

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

Input validation can reject or constrain data that would otherwise drive unbounded recursive calls.

System monitoring can observe anomalous resource consumption that signals runaway recursion after it begins.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

blocks

Secure development life cycle requires controls that prevent uncontrolled recursion through design and code review.

blocks

A.8.26 only requires that security requirements (including resilience against attacks such as buffer overflows) be identified and specified during development or acquisition; it does not itself enforce, implement, or prevent uncontrolled recursion from being exploitable in the resulting application.

blocks

A.8.27 mandates establishing and applying secure engineering principles (defense-in-depth, least privilege, security by design, input distrust, hardening, design reviews) but does not itself stop uncontrolled recursion from being introduced or from consuming excessive resources when present; the weakness can still be exploited.

prevents

Secure coding standards directly prohibit or constrain recursive constructs that could exhaust stack or memory.

finds

Security testing in development can detect excessive recursion via static analysis or fuzzing.

finds

Capacity management includes monitoring and limits that mitigate resource exhaustion from runaway recursion.

Hardening callouts derived

DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.

  • No fine-grained STIG row for CWE-674, a class-level weakness, and none of its children carries one either.

References