# CVE-2026-61674: Fluent Bit: Remote stack buffer overflow in Fluent Bit `out_forward` Secure-Forward `PONG` handler

> Remote attackers can trigger a stack buffer overflow in Fluent Bit's Secure Forward handler, potentially achieving code execution or causing denial of service.

- **Severity:** Critical 9.2 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 Sep 2026
- **Updated:** 21 Sep 2026
- **Also known as:** AZL-105060, BIT-fluent-bit-2026-61674, GHSA-jrp8-r9hx-gf73

## What is CVE-2026-61674?

CVE-2026-61674 is a critical memory corruption vulnerability in fluent-bit, published on 21 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-787 (Out-of-bounds Write), CWE-843 (Access of Resource Using Incompatible Type), CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2026-61674?

1 open source package ship an affected version, including fluent-bit.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `fluent-bit` | Bitnami | From 0.11.0 | 5.0.8 |

## How do I fix CVE-2026-61674?

Upgrade fluent-bit to 5.0.8 or later.

## Is CVE-2026-61674 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-61674 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-61674 and fix it if it is affected.

What it is: CVE-2026-61674 is a critical memory corruption vulnerability in fluent-bit, published on 21 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-61674 exists.

Affected packages and fixed versions:
- fluent-bit (Bitnami): affected from 0.11.0; fixed in 5.0.8

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-61674/ (Markdown: https://insights.sbomify.com/CVE-2026-61674/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-61674
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-61674
- OSV: https://osv.dev/vulnerability/CVE-2026-61674

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-61674/
Summaries are generated and may contain mistakes; the official description above is the record.