CVE-2026-115778
Description
A flaw was found in Twisted. The Telnet service implementation fails to enforce a size limit on incoming data buffers during protocol option negotiation, which occurs before user authentication. An unauthenticated remote attacker can exploit this vulnerability by sending a continuous stream of subnegotiation data without a terminating delimiter. This causes unbounded memory consumption that can crash the application, resulting in a Denial of Service (DoS).
Statement
This vulnerability is rated as an Important impact for Red Hat environments because remote unauthenticated actors can induce complete denial of service through unbounded process memory consumption over a single network connection. Exploitation requires the target environment to actively host and expose a Twisted-based Telnet transport or debugging service. Default deployments of Red Hat products that include Twisted, including Red Hat Ansible Automation Platform and Red Hat OpenStack Platform, do not configure or expose Telnet endpoints, significantly reducing overall exposure in standard installations.
Mitigation
--- CME Mitigation Guidance (2026-11-02) ---
Disclaimer: The following mitigation solutions are provided as a courtesy, pending the application of an official patch. This content was generated utilizing AI tools in conjunction with data from https://cmetaxonomy.org. Customers are advised to independently evaluate and test these temporary mitigations within their own infrastructure.
The highest-value action is to enforce maximum byte size bounds on incoming Telnet subnegotiation buffers in twisted.conch.telnet and terminate connections exceeding the limit: upgrade to Twisted 26.10.0rc1 (or the fixed Python Twisted/Python3X Twisted/Ansible Automation Platform 25/Lightspeed Rhel/Python3.11 Twisted/Python3.12 Twisted/Ansible Automation Platform 24/Controller Rhel/Ansible Automation Platform 25/Controller Rhel/Ansible Automation Platform 26/Controller Rhel/Ansible Automation Platform 26/Eda Controller Rhel/Ansible Automation Platform 27/Eda Controller Rhel/Automation Controller/Ansible Automation Platform 27/Controller Rhel/Ansible Automation Platform 26/Lightspeed Rhel/Ansible Automation Platform 27/Lightspeed Rhel/Ansible Ai Connect Service builds), which enforce a 4096-byte limit on subnegotiation data and drop the connection when the limit is exceeded, closing continuous streaming of unterminated Telnet subnegotiation payload. Until patched, this is a concern on deployments actively hosting and exposing an unauthenticated Twisted-based Telnet transport or debugging service, so restrict network access to exposed Twisted Telnet endpoints via firewall rules and disable unused Telnet or manhole debugging services. As a compensating measure, monitor cgroup memory pressure using memory.events and PSI to detect rapid memory growth from unterminated subnegotiation streaming, restrict maximum address space using ulimit or prlimit RLIMIT_AS to prevent host-level memory exhaustion, configure systemd WatchdogSec and Restart directives to automatically restart the Twisted service upon out-of-memory termination, and apply cgroups v2 resource limits to constrain memory allocation and prevent process memory growth from exhausting host resources. These controls limit blast radius and contain exploitation, but they do not fix the underlying unbounded subnegotiation buffer defect — apply the upstream patch to fully remediate.
Highest-impact CME: CME-1311 Input Size and Quantity Bounds Enforcement (high)
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); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other)
When allocating resources without limits, an attacker could prevent other systems, applications, or processes from accessing the same type of resource. It can be easy for an attacker to consume many resources by rapidly making many requests or causing larger resources to be used than is needed.
Frequently Asked Questions
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