CVE-2026-104020: Uncontrolled recursion in the Ion reader in Amazon Ion Python

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-01 · updated 2026-10-02
Weakness: CWE-674

Description

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

Affected products

Amazon ion-python: before 0.15.0 — fixed in 0.15.0

How to fix

Upgrade to a fixed version: Amazon ion-python 0.15.0. Check the vendor advisory for mitigations.

References

https://aws.amazon.com/security/security-bulletins/2026-122-aws/
https://github.com/amazon-ion/ion-python/releases/tag/v0.15.0
https://github.com/amazon-ion/ion-python/security/advisories/GHSA-93q6-f8hx-vv7f

Get alerted when CVE-2026-104020 or the next vulnerability affects your stack