CVE-2026-55255 is a critical-severity security vulnerability in langflow (pip), affecting versions < 1.9.1. It is fixed in 1.9.1.
Summary Insecure Direct Object Reference (IDOR) vulnerability in /api/v1/responses endpoint allows an authenticated attacker to execute any flow belonging to another user by specifying the victim's flow ID in the request. Details The vulnerability exists in the getflowbyidorendpointname helper function in src/backend/base/langflow/helpers/flow.py (lines 399-414). When a flow is accessed via UUID (flowid), the function queries the database directly without verifying if the authenticated user owns that flow: This function is used by the /api/v1/responses endpoint (defined in src/backend/base/langflow/api/v1/openairesponses.py:589). PoC (Proof of Concept) Impact Any authenticated user can: Execute any flow in the system by knowing its flow ID Access potentially sensitive data processed by victim's flows Consume victim's resources Fixes Fixed in PR #12832 (fix(security): close IDOR in getflowbyidorendpointname), merged 2026-04-22, released in Langflow 1.9.1. The helper normalizes userid once and enforces ownership on both lookup branches (UUID and endpointname): Key points: Cross-user lookups return 404 (not 403), so flow existence is not disclosed via a 403-vs-404 oracle. /api/v1/responses and /api/v2/workflow pass userid explicitly, so fixing the helper closes them directly; the /api/v1/run routes were additionally moved from a bare Depends(getflowbyidorendpointname) to auth-aware wrapper dependencies (defense in depth). A malformed user_id now fails closed (404 instead of a raw 500). Webhook routes intentionally keep the unscoped lookup (public by design / explicit ownership check elsewhere). Regression tests cover the cross-user UUID case and reproduce the original PoC against /api/v1/responses. Acknowledgements Thanks to the security researchers who responsibly disclosed this vulnerability: @yzeirnials @johnatzeropath @LeftenantZero @Zwique
CVE-2026-55255 has a CVSS score of 9.9 (Critical). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment.
A fixed version is available (1.9.1). Upgrading removes the vulnerable code path.
pip
langflow (< 1.9.1)langflow → 1.9.1 (pip)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Upgrade langflow to 1.9.1 or later to resolve this vulnerability.
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CVE-2026-55255 is a critical-severity security vulnerability in langflow (pip), affecting versions < 1.9.1. It is fixed in 1.9.1.
CVE-2026-55255 has a CVSS score of 9.9 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
langflow (pip) versions < 1.9.1 is affected.
Yes. CVE-2026-55255 is fixed in 1.9.1. Upgrade to this version or later.
Whether CVE-2026-55255 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
Upgrade langflow to 1.9.1 or later.