EUVD Vulnerability Catalog

EUVD-2026-83985

Severity: CRITICAL Base Score: 9.2 CVSS Version: 4.0

Vulnerability Description

Fluent Bit is a fast and lightweight logs, metrics, and traces processor for Linux, BSD, macOS, and Windows. From 0.11.0 until 5.0.8, plugins/out_forward/forward.c secure_forward_pong copies the server-controlled PONG[2] reason into the 32-byte stack buffer msg with memcpy without checking its MessagePack type or length. An attacker who controls or can impersonate an out_forward Secure Forward destination configured with Shared_Key or Empty_Shared_Key can send an oversized reason during the first handshake and overwrite stack control data. Protected builds reliably terminate, while builds without a stack canary or with a disclosure can allow remote code execution as the Fluent Bit process user. When the opt-in --supervisor mode is used, fork-only respawns preserve the canary and address layout, allowing repeated crash-or-survive probes to support code execution on a hardened build; ordinary exec-based or service-manager restarts do not preserve that state. This issue is fixed in version 5.0.8.

CVSS Vector Analysis

Below is the complete, human-readable breakdown of the CVSS metric string: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

▪ Attack Vector (AV): Network

▪ Attack Complexity (AC): Low

▪ Attack Requirements (AT): Present

▪ Privileges Required (PR): None

▪ User Interaction (UI): None

▪ Vulnerability Confidentiality Impact (VC): High

▪ Vulnerability Integrity Impact (VI): High

▪ Vulnerability Availability Impact (VA): High

▪ Subsequent Confidentiality Impact (SC): None

▪ Subsequent Integrity Impact (SI): None

▪ Subsequent Availability Impact (SA): None

Affected Vendors & Systems

Vendor fluent

References & Advisory Links

Metadata Profile

Database Authority

European Union Agency for Cybersecurity (ENISA) EUVD

Assigner

GitHub_M

EPSS Probability

Known Aliases

CVE-2026-61674

Published On

2026-09-21

Last Updated

2026-09-21