CVE-2026-55255
Langflow Authorization Bypass Through User-Controlled Key Vulnerability
Description
CVE-2026-55255 is a high-severity Insecure Direct Object Reference (IDOR) vulnerability in Langflow, an open-source tool for building and deploying AI-powered agents and workflows. In versions before 1.9.1, the /api/v1/responses endpoint fails to verify object-level authorization, so an authenticated attacker can execute any flow belonging to another user simply by supplying the victim's flow ID in the request. This authorization bypass carries a CVSS score of 8.4 (High) and can expose other users' data and let attackers trigger workflows they should not control. CISA has added CVE-2026-55255 to its Known Exploited Vulnerabilities (KEV) catalog, and the flaw is fixed in Langflow 1.9.1, so upgrading is strongly recommended.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:LOpen in CalculatorCWEs
Affected Products
| Vendor | Product | Version |
|---|---|---|
| langflow | langflow | < 1.9.1 |
References
- https://github.com/langflow-ai/langflow/commit/2c9f498d664a3c32698b57d7c5e752625291060e(Patch)
- https://github.com/langflow-ai/langflow/pull/12832(Issue Tracking, Patch)
- https://github.com/langflow-ai/langflow/security/advisories/GHSA-qrpv-q767-xqq2(Exploit, Mitigation, Vendor Advisory)
- https://webflow.sysdig.com/blog/understanding-langflow-cve-2026-55255-and-why-higher-cvss-vulnerabilities-arent-always-the-most-exploited(Third Party Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55255(US Government Resource)
Weakness Type
CWE-639: Authorization Bypass Through User-Controlled Key
This weakness occurs when Langflow's authorization logic does not stop one user from accessing another user's resources by changing the key value that identifies them — the classic Insecure Direct Object Reference (IDOR) pattern. In Langflow it manifests on the /api/v1/responses endpoint, which trusts the user-supplied flow ID without checking that the authenticated caller actually owns that flow.
Learn more: CWE-639 — Authorization Bypass Through User-Controlled Key
Impact Analysis
CVE-2026-55255 is rated High with a CVSS 3.1 score of 8.4. The vulnerability is remotely exploitable over the network but requires some low-level privileges — the attacker must be authenticated (Privileges Required Low) — and the attack complexity is High, meaning specific conditions must be met, though no user interaction is required. Critically, the scope is Changed, so exploitation can affect resources beyond the vulnerable component and reach flows owned by other users. The High confidentiality and integrity impacts mean an attacker can access sensitive data processed by another user's flow and tamper with its execution, while the availability impact is Low. Because CISA lists this in its KEV catalog, active exploitation is confirmed and remediation should not be delayed.
Exploit Maturity
CISA has confirmed active exploitation of CVE-2026-55255 in the wild by adding it to the Known Exploited Vulnerabilities catalog, so defenders should prioritize it. The vendor security advisory, which is tagged as containing exploit and mitigation details, is publicly available via GitHub Security Advisory GHSA-qrpv-q767-xqq2, and the fix is published in the linked patch commit and pull request. The EPSS score of about 0.6% (43rd percentile) is relatively low, but the confirmed KEV listing outweighs the statistical estimate; ransomware use is currently listed as Unknown. Given a public advisory and a straightforward IDOR pattern, organizations running Langflow before 1.9.1 should upgrade without delay.
Remediation
- Follow CISA's KEV required action: apply mitigations in accordance with vendor instructions and ensure compliance with CISA's BOD 26-04 patching guidance; discontinue use if mitigations are unavailable. The remediation due date was 2026-07-10.
- Upgrade Langflow to version 1.9.1 or later, in which this IDOR is fixed; all versions before 1.9.1 are affected.
- As an interim mitigation, restrict network access to the Langflow instance and the
/api/v1/responsesendpoint, and limit which authenticated accounts can reach the API. - Review access logs for requests to
/api/v1/responsesthat reference flow IDs not owned by the requesting user, which may indicate attempts to execute other users' flows. - As long-term hardening, enforce object-level authorization checks that verify the authenticated user owns the requested flow, use indirect references mapped server-side to real objects, and treat every user-supplied identifier as untrusted.
Technical Details
The root cause of CVE-2026-55255 is CWE-639, an authorization bypass through a user-controlled key: the /api/v1/responses endpoint uses the client-supplied flow ID to select and execute a flow without confirming the authenticated caller is authorized for that specific object, the defining trait of an IDOR. Exploitation is performed over the network (AV:N) by a low-privileged authenticated user (PR:L) with no user interaction (UI:N), but the High attack complexity (AC:H) reflects that additional conditions must be satisfied, which is why the CVSS 3.1 vector CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L scores 8.4. The Changed scope (S:C) captures that the impact crosses the authorization boundary into resources belonging to other users.
Frequently Asked Questions
Is CVE-2026-55255 being actively exploited?
Yes. CISA has added CVE-2026-55255 to its Known Exploited Vulnerabilities catalog, confirming exploitation in the wild. A public GitHub Security Advisory with exploit and mitigation details is available, while ransomware association is currently listed as Unknown.
What products are affected by CVE-2026-55255?
The vulnerability affects Langflow, the open-source tool for building and deploying AI-powered agents and workflows, in all versions before 1.9.1. The issue is fixed in Langflow 1.9.1.
How do I fix CVE-2026-55255?
Upgrade Langflow to version 1.9.1 or later, where the IDOR on the /api/v1/responses endpoint is resolved. In the interim, restrict network access to the API, and review logs for requests referencing flow IDs the caller does not own.
How severe is CVE-2026-55255?
It is rated High with a CVSS 3.1 score of 8.4. The high confidentiality and integrity impact, combined with a Changed scope that reaches other users' flows and confirmed active exploitation in CISA's KEV catalog, makes it a serious risk despite its comparatively low EPSS percentile.
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