CVE-2026-19306: 
Homebrew vulnerability analysis and mitigation

CVE-2026-19306 is a path traversal vulnerability in IBM Langflow OSS (versions 1.0.0 through 1.11.2) that allows authenticated attackers to read arbitrary files from the server filesystem. Sensitive material including secret keys, JWT signing keys, the application database, /proc/self/environ, and other tenants' upload directories can be accessed by supplying absolute paths or traversal sequences in the files parameter of a build request. The vulnerability was published on September 4, 2026, with a patch reference added on September 8, 2026. It carries a CVSS v3.1 base score of 7.7 (High) (Feedly, IBM Advisory).

The root cause is CWE-22 (Improper Limitation of a Pathname to a Restricted Directory — Path Traversal). An authenticated attacker submits a crafted build request with absolute paths or ../ traversal sequences in the files parameter of the Chat Input to Message attachment pipeline. The file contents are then embedded as text attachments in the language model prompt and transmitted to the configured model endpoint, effectively exfiltrating the data. Critically, this attack vector bypasses the LANGFLOW_RESTRICT_LOCAL_FILE_ACCESS=true containment boundary, which was enforced for other file-reading components but not for this specific pipeline (Feedly).

Successful exploitation allows a low-privileged authenticated attacker to exfiltrate highly sensitive server-side data, including cryptographic secrets (secret_key, JWT signing keys), the application database, environment variables (/proc/self/environ), and upload directories belonging to other tenants. Because the exfiltrated data is transmitted to an external language model endpoint, the confidentiality breach extends beyond the server boundary. Compromise of JWT signing keys could enable token forgery and full account takeover, while exposure of the application database could affect all users of the platform. The scope is rated as Changed, indicating impact beyond the vulnerable component itself (Feedly).

As of the time of reporting, there is no public proof-of-concept exploit and no evidence of in-the-wild exploitation (Feedly). The NVD SSVC assessment classifies exploitation as "none" and the attack as non-automatable, as it requires authenticated access with low privileges. The EPSS score is approximately 0.41%, indicating a low near-term exploitation probability. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog (Feedly).

1. Authentication: Obtain valid credentials for an IBM Langflow OSS instance (version 1.0.0–1.11.2) with at least low-privilege access.
2. Identify the build endpoint: Locate the authenticated API endpoint used to submit build requests that accept a files parameter (part of the Chat Input to Message attachment pipeline).
3. Craft a malicious request: Construct a build request where the files parameter contains an absolute path (e.g., /etc/passwd, /proc/self/environ, or the Langflow secret_key file) or a path traversal sequence (e.g., ../../etc/shadow).
4. Submit the request: Send the crafted request to the Langflow server. The server reads the specified file and embeds its contents as a text attachment in the language model prompt.
5. Retrieve exfiltrated data: The file contents are transmitted to the configured language model endpoint. The attacker can intercept or retrieve this data from the model's response or by controlling/monitoring the model endpoint.
6. Escalate: Use recovered secrets (e.g., JWT signing keys) to forge authentication tokens, access other tenants' data, or pivot to further compromise (Feedly).

• Network: Outbound connections from the Langflow server to the configured language model endpoint containing unusual or large text payloads (file contents embedded in prompts); unexpected API calls to the build endpoint from low-privilege accounts.
• Logs: Application logs showing build requests with files parameter values containing absolute paths (e.g., /etc/, /proc/, /app/) or traversal sequences (../); repeated or automated build requests from a single authenticated user.
• File System: No direct file system artifacts are created by the attacker, but access timestamps on sensitive files (e.g., secret_key, application database, /proc/self/environ) may be updated unexpectedly.
• Process Behavior: Langflow process reading files outside its expected working directory or upload folder, observable via OS-level file access auditing (e.g., auditd on Linux) (Feedly).

IBM has released a fix; users should upgrade IBM Langflow OSS to version 1.11.3 or later (IBM Advisory). As interim mitigations, implement strict server-side input validation on the files parameter of build requests to reject absolute paths and traversal sequences. Ensure LANGFLOW_RESTRICT_LOCAL_FILE_ACCESS=true is consistently enforced across all file-reading components, including the Chat Input to Message attachment pipeline. Additionally, consider network segmentation to restrict outbound connections from the Langflow server to the language model endpoint, reducing the risk of data exfiltration (Feedly).

The vulnerability received limited but notable coverage shortly after disclosure, with mentions on Mastodon via TheHackerWire and tracking by threat intelligence aggregators including VulDB, Radar Offseq, and CVE Threat Intel (Feedly). No significant vendor statements beyond the IBM advisory or prominent researcher commentary have been identified at this time.