Fluent Bit: Remote stack buffer overflow in Fluent Bit `out_forward` Secure-Forward `PONG` handler (CVE-2026-61674) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-61674

Fluent Bit: Remote stack buffer overflow in Fluent Bit `out_forward` Secure-Forward `PONG` handler

Answer in brief

CVE-2026-61674 records a Unknown severity vulnerability in Fluent Bit: Remote stack buffer overflow in Fluent Bit `out_forward` Secure-Forward `PONG` handler. The current sources do not mark it as known exploited. The current feed maps fluent/fluent-bit (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 21, 2026Updated Sep 21, 2026Source checked Sep 21, 2026First seen by HOL Sep 21, 2026Material review Sep 21, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps fluent/fluent-bit (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
fluent/fluent-bitgeneric	>= 0.11.0, < 5.0.8	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for fluent/fluent-bit.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Sep 21, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 21, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 21, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.