CVE-2026-94135 Overview
CVE-2026-94135 affects the Apache Airflow SFTP provider's deferrable code paths. The SFTPTrigger, SFTPHookAsync, and SFTPClientPool components disable SSH host-key verification by default. Verification only occurs when a connection explicitly sets no_host_key_check to false. Deployments running SFTP sensors or operators in deferrable mode are exposed.
An attacker positioned between the Airflow triggerer and the SFTP server can impersonate the server. The attacker can then capture credentials or data exchanged during the session. The flaw is classified under [CWE-322: Key Exchange without Entity Authentication].
Critical Impact
A machine-in-the-middle attacker can intercept SFTP credentials and transferred data when Airflow runs SFTP tasks in deferrable mode.
Affected Products
- Apache Airflow SFTP Provider (apache-airflow-providers-sftp) versions prior to 7.0.0
- Airflow deployments using SFTPTrigger in deferrable mode
- Airflow deployments using SFTPHookAsync or SFTPClientPool
Discovery Timeline
- 2026-10-15 - CVE-2026-94135 published to NVD
- 2026-10-16 - Last updated in NVD database
Technical Details for CVE-2026-94135
Vulnerability Analysis
The Apache Airflow SFTP provider offers both synchronous and deferrable execution paths. The deferrable code paths — SFTPTrigger, SFTPHookAsync, and SFTPClientPool — initialize SSH sessions with host-key verification disabled by default. This inverts the secure-by-default expectation set by the underlying SSH libraries.
Operators who deploy SFTP sensors or operators in deferrable mode inherit the insecure default. Unless the connection configuration explicitly sets no_host_key_check to false, the triggerer accepts any server key presented. The result is silent trust of unverified SFTP endpoints during asynchronous task execution.
This defect is distinct from CVE-2026-94134, which covers the synchronous SSH hook default. Fixing one does not address the other. The maintainers consolidated both fixes in apache-airflow-providers-sftp 7.0.0.
Root Cause
The root cause is an insecure default configuration in the deferrable SFTP code paths. Host-key verification is opt-in rather than opt-out, which violates standard SSH trust model expectations. The affected classes do not enforce known_hosts validation when establishing asynchronous SFTP sessions.
Attack Vector
Exploitation requires network-adjacent positioning between the Airflow triggerer and the target SFTP server. An attacker intercepts the SFTP connection, presents a fraudulent host key, and completes the handshake with the triggerer. Because host-key verification is disabled, the triggerer proceeds with authentication and data transfer. The attacker captures user credentials and any file contents transferred during the session.
The vulnerability does not grant code execution. It compromises confidentiality and integrity of SFTP sessions established through deferrable operators.
Detection Methods for CVE-2026-94135
Indicators of Compromise
- Unexpected SSH host-key fingerprints observed in triggerer logs for SFTP connections
- SFTP connections from Airflow triggerer hosts to IP addresses outside the documented SFTP server range
- Authentication failures on the legitimate SFTP server coinciding with successful transfers reported by Airflow
- Airflow connections configured without an explicit no_host_key_check=false setting on deferrable SFTP tasks
Detection Strategies
- Inventory all Airflow DAGs that use SFTPTrigger, SFTPHookAsync, or SFTPClientPool in deferrable mode
- Audit apache-airflow-providers-sftp package versions across triggerer and worker nodes for versions below 7.0.0
- Review Airflow connection extras to confirm no_host_key_check is explicitly set to false and host_key is populated
Monitoring Recommendations
- Enable network flow logging between Airflow triggerer nodes and SFTP endpoints to detect redirected traffic
- Alert on new or unexpected SSH host keys presented to Airflow triggerer processes
- Correlate SFTP task execution logs with SFTP server authentication logs to detect session mismatches
How to Mitigate CVE-2026-94135
Immediate Actions Required
- Upgrade apache-airflow-providers-sftp to version 7.0.0 or later on all triggerer and worker nodes
- Set no_host_key_check=false and populate host_key on every Airflow SFTP connection
- Rotate any SFTP credentials used by deferrable SFTP tasks because prior sessions may have been intercepted
- Review the related advisory for CVE-2026-94134 and confirm both fixes are applied
Patch Information
Upgrade to apache-airflow-providers-sftp 7.0.0 or later. This release fixes both CVE-2026-94135 and the related synchronous SSH hook defect CVE-2026-94134. Technical details are available in the Apache Airflow Pull Request #73419 and the Apache mailing list announcement.
Workarounds
- Disable deferrable mode on SFTP sensors and operators until the upgrade is applied
- Explicitly set no_host_key_check=false on every SFTP connection and provide the expected host_key
- Restrict triggerer network egress to known SFTP server IP addresses using firewall rules
- Terminate SFTP traffic through a trusted bastion or proxy that enforces host-key pinning
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
