CVE-2026-42359: Apache Airflow: Authenticated RCE via XCom PATCH endpoint — XComUpdateBody missing FORBIDDEN_XCOM_KEYS validator

[Rahul Vats <rahulvats () apache org>]

Severity: medium 

Affected versions:

- Apache Airflow (apache-airflow) 3.2.0 before 3.2.2

Description:

A bug in Apache Airflow's XCom PATCH endpoint `PATCH /api/v2/xcomEntries/{key}` allowed an authenticated UI/API user 
with XCom write permission on a Dag to set XCom entries under reserved key names (e.g. `return_value`) that the 
matching POST endpoint already validated against `FORBIDDEN_XCOM_KEYS`. The endpoint also accepted serialized payload 
shapes the triggerer's deserializer treats as code; combined, this allowed RCE on the triggerer when the affected task 
next deferred. Affects deployments where untrusted users have XCom write permission on Dags that defer to the 
triggerer. This is a fix-bypass of CVE-2026-33858: PR #64148 added the `FORBIDDEN_XCOM_KEYS` validator only on the 
POST/set path; the PATCH path was not covered. Users who already upgraded for CVE-2026-33858 should additionally 
upgrade to `apache-airflow` 3.2.2 or later to cover the PATCH-path bypass.

Credit:

Jeff Vier (`@boinger`); Izat (Anisto Mejin) — placeholders; receipt-of-confirmation replies ask each reporter to 
confirm preferred credit form (finder)
Venkatraman Kumar (r3dw0lfsec), Securin (finder)
Jarek Potiuk (remediation developer)

References:

https://github.com/apache/airflow/pull/65915
https://airflow.apache.org/
https://www.cve.org/CVERecord?id=CVE-2026-42359