CVE-2026-55255: Langflow IDOR in responses endpoint allows cross-user flow execution

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 17 September 2026. Confidence: high.

high priorityCISA KEV listing with a short remediation deadline signals confirmed exploitation, though the high attack complexity and low EPSS temper the rating below critical.

What it is

Langflow before 1.9.1 has an insecure direct object reference in the /api/v1/responses endpoint. An authenticated attacker can supply another user's flow ID and execute that flow, crossing a tenant/user boundary. It matters because flow execution can run attacker-influenced logic under the victim's identity and resources.

Impact

An authenticated attacker gains the ability to execute any flow owned by another user, potentially running workflows with the victim's credentials, data and connected integrations. The CVSS vector rates high confidentiality and integrity impact with limited availability impact.

Attack surface

Reachable over the network via the /api/v1/responses API endpoint. Authentication is required (PR:L) and no user interaction is needed (UI:N); the attacker only needs to know or guess a victim flow ID.

Exploitation

CVE-2026-55255 was added to CISA KEV on 2026-07-07 with a 2026-07-10 due date, indicating known exploitation, while EPSS 30-day probability is low at 0.00887 (57th percentile). Vendor advisory references are tagged Exploit.

What to do

• Upgrade Langflow to 1.9.1 or later, which contains the fix.
• If immediate upgrade is not possible, restrict network access to the /api/v1/responses endpoint and follow CISA BOD 26-04 guidance, discontinuing use if mitigations are unavailable.
• Enforce server-side ownership checks so flow IDs are validated against the authenticated user before execution.
• Audit and rotate credentials or API keys reachable by flows that may have been executed by unauthorized users.
• Monitor for anomalous flow executions referencing flow IDs not owned by the requesting account.

Detection

• Review Langflow API logs for /api/v1/responses requests where the flow ID owner differs from the authenticated caller.
• Alert on a single account executing a high number of distinct flow IDs or flow IDs outside its normal set.
• Correlate flow execution events with source IPs and user agents that are new for the account.
• Check for outbound connections or credential use from flows that the owner did not trigger.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.