Amazon Ion Python: Denial of service via uncontrolled recursion in Ion reader
Summary
Amazon Ion Python, an open-source Python implementation of the Amazon Ion data notation, contains an uncontrolled recursion flaw in its Ion reader. A remote, unauthenticated attacker can supply a crafted, deeply nested Ion value that crashes the application using the library, causing a denial of service. The risk applies only where an application parses Ion data from untrusted sources.
Affected
- ion-python versions before 0.15.0
- Vendor range: < 0.15.0 (default: unaffected)
Fixed in
- Fixed in ion-python version 0.15.0
- Forks and derivative code must also be patched with the new fixes according to the vendor
Workaround
- Disable the C extension (simpleion.c_ext = False) and explicitly handle RecursionError raised from within the simpleion module. This is a stopgap; the upgrade is the vendor's recommended fix.
Exploitation
- No evidence of exploitation in the wild found.
- No public proof of concept found.
- CISA SSVC: Exploitation none, automatable yes, technical impact partial.
- EPSS 0.00441 (low predicted exploitation likelihood).
Our recommendation
- Check Python environments and requirements files for ion-python (for example with pip show ion-python).
- Identify internet-facing services that parse Ion data from untrusted sources.
- Upgrade to ion-python 0.15.0 or later, including any forked or vendored copies.
- Where the upgrade is delayed, apply the configuration workaround and monitor for process restarts.
- Priority: low to medium for most SMEs, higher where untrusted Ion input is parsed.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- AWS Security Bulletin 2026-122-AWS aws.amazon.com
- GitHub Security Advisory GHSA-93q6-f8hx-vv7f github.com
- ion-python Release v0.15.0 github.com
- OSV CVE-2026-104020 osv.dev
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 06:16.
Original description (NVD)
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.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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