CVE-2026-126080
Description
A flaw was found in Active Support. An unauthenticated remote attacker can cause a Denial of Service (DoS) by submitting crafted input that is handled during constant lookup, such as through channel subscription requests. Because untrusted constant names are compiled into regular expressions without proper sanitization, specially constructed input can crash the underlying server process and render the application unavailable.
Statement
This vulnerability is rated as Important because an unauthenticated remote attacker can crash the application server by providing malicious channel subscription parameters to exposed Action Cable endpoints, causing a persistent denial of service. The impact primarily threatens availability in deployments that permit unauthenticated connections to Action Cable endpoints. Services that disable Action Cable or enforce strict user verification prior to channel subscription face significantly reduced exposure.
Mitigation
For applications that do not require Action Cable functionality, disable the endpoint by setting the mount path to nil in the application configuration:
config.action_cable.mount_path = nil
For applications requiring Action Cable, enforce authentication by rejecting unauthorized connections in the connection handler:
# In app/channels/application_cable/connection.rb
module ApplicationCable
class Connection < ActionCable::Connection::Base
def connect
reject_unauthorized_connection unless current_user
end
end
end
Caveats: Disabling the mount path disables all Action Cable WebSocket endpoints. Enforcing authentication limits exposure to verified users only and does not eliminate risk from untrusted authenticated users.
Warning: Modifying application configuration or channel connection files requires restarting the application service to take effect.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU)
Attackers can create crafted inputs that intentionally cause the regular expression to use excessive backtracking in a way that causes the CPU consumption to spike.
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