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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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.
Which versions are affected by CVE-2026-61674?
1 open source package ship an affected version, including fluent-bit.
| Package | 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.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-61674 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-61674 exists.
Sources
Also known as AZL-105060, BIT-fluent-bit-2026-61674, GHSA-jrp8-r9hx-gf73.