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CVE-2026-42359 Apache Software Foundation CVE debrief

A fix-bypass vulnerability in Apache Airflow's XCom PATCH endpoint allows authenticated users with XCom write permissions to set reserved key names (e.g., `return_value`) that were blocked in the POST endpoint by the `FORBIDDEN_XCOM_KEYS` validator added in CVE-2026-33858. The PATCH endpoint's missing validation, combined with acceptance of serialized payload shapes that the triggerer's deserializer treats as code, enables remote code execution on the triggerer when an affected task next defers. This affects deployments where untrusted users hold XCom write permissions on DAGs that defer to the triggerer. Users who applied the CVE-2026-33858 fix must additionally upgrade to `apache-airflow` 3.2.2 or later to close this bypass.

Vendor
Apache Software Foundation
Product
Apache Airflow
CVSS
HIGH 8.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-01
Original CVE updated
2026-07-21
Advisory published
2026-06-01
Advisory updated
2026-07-21

Who should care

Organizations running Apache Airflow 3.x deployments with multi-tenant or untrusted user access, particularly those using deferred tasks and the triggerer component. Security teams responsible for supply chain and data pipeline security should prioritize this fix-bypass even if CVE-2026-33858 was previously addressed.

Technical summary

The `PATCH /api/v2/xcomEntries/{key}` endpoint in Apache Airflow fails to validate against `FORBIDDEN_XCOM_KEYS`, allowing authenticated users with XCom write permissions to modify reserved keys like `return_value`. Combined with acceptance of serialized payloads that the triggerer deserializes as executable code, this results in remote code execution on the triggerer during task deferral. The vulnerability exists because CVE-2026-33858's fix (PR #64148) only covered the POST/set path. Resolution requires upgrading to apache-airflow 3.2.2+ where PR #65915 extends validation to the PATCH path.

Defensive priority

critical

Recommended defensive actions

  • Upgrade to apache-airflow 3.2.2 or later to obtain the PATCH-path `FORBIDDEN_XCOM_KEYS` validation
  • Audit and restrict XCom write permissions to trusted users only, particularly on DAGs that use deferral/triggerer patterns
  • Review existing XCom entries for unauthorized modifications to reserved keys such as `return_value`
  • If immediate patching is not feasible, consider network segmentation to limit triggerer exposure and monitor for anomalous XCom PATCH operations
  • Verify that prior CVE-2026-33858 mitigations are in place and do not rely solely on POST endpoint validation

Evidence notes

The vulnerability is a fix-bypass of CVE-2026-33858: PR #64148 added `FORBIDDEN_XCOM_KEYS` validation only on the POST/set path, leaving the PATCH path uncovered. The CWE-502 classification indicates deserialization of untrusted data. The fix is tracked in PR #65915.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-42359 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-42359

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-42359 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-42359

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.