[OSSN-0099] Denial of Service in OpenStack Ironic under reduced process stack size (CVE-2026-50589)

[Jay Faulkner <jay () jvf cc>]

Denial of Service in Ironic under reduced process stack size
---

### Summary ###
An unauthenticated malicious user could submit a specially crafted
JSON string to certain endpoints on the API service or the JSON-RPC
endpoint if enabled, and cause a service crash until the service is
restarted. This was due to the memory allocation exceeding the stack
size of the Python runtime due to Ironic's reduced default stack size
prior to the initial payload validation.

### Affected Services / Software ###
- ironic: >=32.0.0, <37.0.0

### Discussion ###
The Ironic project has introduced a customized size check
middleware which looks for excessive and invalid recursive JSON data
structures while also enforcing path awareness and endpoint size limits
based upon the intended patterns of interaction with Ironic.

### Recommended Actions ###
Apply the provided Ironic patches.

Review the newly provided configuration variables defaults in context of 
your
cluster.

Several options were added related to permitted JSON body sizing. The 
defaults
should be sufficient for most clouds but can be adjusted:
- '[api]/max_json_body_depth', default 25, will reject requests with JSON
  documents with more recursion depth than this.
- '[api]/max_json_body_size', default 1024, is the maximum size, in KiB, the
  API service will accept for any endpoint except the node provision 
state and
  continue_inspection endpoints. Requests with a larger content-length will
  receive an HTTP 413 response.
- '[api]/max_json_body_size_provision', default 65536 (64MiB), is the 
max size,
  in KiB, for the node provision state endpoint. The larger default is 
due to
  the need to accomodate configdrives or deploy_steps.
- '[api]/max_json_body_size_inspection', default 16384 (16MiB), is the max
  size, in KiB, for the continue_inspection endpoint. The larger default is
  due to the need to accomodate inspection data from the ramdisk, which can
  include system logs and data larger than normal API requests.

Operators unable or unwilling to patch their Ironic installations can work
around the issue by increasing the process stack size by setting the
environment variable 'IRONIC_THREAD_STACK_SIZE=8388608' before starting 
Ironic
services.

#### Patches ####
The following reviews contain the fix for this issue:

2026.2/hibiscus (master): 
https://review.opendev.org/c/openstack/ironic/+/991717
2026.1/gazpacho: https://review.opendev.org/c/openstack/ironic/+/991854
2025.2/flamingo: https://review.opendev.org/c/openstack/ironic/+/991858
bugfix/34.0: https://review.opendev.org/c/openstack/ironic/+/991856
bugfix/33.0: https://review.opendev.org/c/openstack/ironic/+/991857

### Credits ###
Dmitry Tantsur, Red Hat
Tuomo Tanskanen, Ericsson Software Technology
Metal3.io Security Team

### Contacts / References ###
Authors:
- Jay Faulkner, G-Research Open Source Software (GR-OSS)
- Julia Kreger, Red Hat

This OSSN: https://wiki.openstack.org/wiki/OSSN/OSSN-0099
Original Launchpad bug: https://bugs.launchpad.net/ironic/+bug/2154288
Mailing List : [security-sig] tag on openstack-discuss () lists openstack org
OpenStack Security : https://security.openstack.org/
CVE: CVE-2026-50589

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