CVE-2026-114550
Description
A flaw was found in libwebsockets. When processing Message Queuing Telemetry Transport (MQTT) publish acknowledgment (PUBACK) packets, incoming network data is not properly validated, resulting in an out-of-bounds memory write. An unauthenticated remote attacker can exploit this vulnerability by sending specially crafted packets to execute arbitrary code in the context of the running application.
Statement
libwebsockets MQTT PUBACK packet handler performs an out-of-bounds write due to incorrect parser-state transition on the property-length VBI; remote unauthenticated attackers who can reach an MQTT-enabled lws endpoint may achieve arbitrary code execution; fixed upstream in commit c9e8e18; CVSS 8.1 IMPORTANT consistent with ZDI-26-792
Mitigation
--- CME Mitigation Guidance (2026-11-04) ---
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 correct parser state transitions during MQTT PUBACK packet property length processing in libwebsockets: upgrade to the fixed Libwebsockets builds, which transition the MQTT parser state to LMQCPP_EAT_PROPERTIES_AND_COMPLETE instead of LMQCPP_PUBACK_VH_PKT_ID and remove variable byte integer tracking re-initialization, closing crafted MQTT PUBACK packets. Until patched, this is a concern on applications utilizing libwebsockets MQTT protocol handling exposed to network access, so restrict network access to applications exposing libwebsockets MQTT endpoints so unauthenticated external traffic cannot reach the parser. As a compensating measure, Randomize memory layout using ASLR to prevent reliable code execution via the out-of-bounds memory write, Enable Full RELRO and PIE to prevent Global Offset Table overwrites and enforce position-independent execution, and Implement Control Flow Integrity or Shadow Call Stack to restrict indirect branch targets and protect return addresses against ROP and JOP payloads. These controls limit blast radius and contain exploitation, but they do not fix the underlying out-of-bounds write defect — apply the upstream patch to fully remediate.
Highest-impact CME: CME-101 ASLR (Address Space Layout Randomization) (medium)
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 | 8.1 | N/A | 8.1 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | High | N/A | High |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Write operations could cause memory corruption. In some cases, an adversary can modify control data such as return addresses in order to execute unexpected code.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
Attempting to access out-of-range, invalid, or unauthorized memory could cause the product to crash.
Other
Technical Impact: Unexpected State
Subsequent write operations can produce undefined or unexpected results.
Frequently Asked Questions
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