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/outforward/forward.c secureforwardpong 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 outforward Secure Forward destination configured with SharedKey or EmptySharedKey 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.
Fluent Bit inhttp, insplunk, and inelasticsearch input plugins contain a flaw in the tagkey validation logic that fails to enforce exact key-length matching. This allows crafted inputs where a tag prefix is incorrectly treated as a full match. A remote attacker with authenticated or exposed access to these input endpoints can exploit this behavior to manipulate tags and redirect records to unintended destinations. This compromises the authenticity of ingested logs and can allow injection of forged data, alert flooding and routing manipulation.
CVE-2025-12977
CVE-2025-12970
An issue in fluent-bit v.3.7.2 allows a local attacker to cause a denial of service via the cfllistsize in cfllist.h:165.
An issue in fluent-bit v.3.7.2 allows a local attacker to cause a denial of service via the function consumeevent.
An issue was discovered in Fluent Bit 3.1.9. When the Prometheus Remote Write input plugin is running and listening on an IP address and port, one can send a packet with Content-Length: 0 and it crashes the server. Improper handling of the case when Content-Length is 0 allows a user (with access to the endpoint) to perform a remote Denial of service attack. The crash happens because of a NULL pointer dereference when 0 (from the Content-Length) is passed to the function cflsdslen, which in turn tries to cast a NULL pointer into struct cflsds. This is related to processpayloadmetricsng() at promrwprot.c.
A memory corruption vulnerability in Fluent Bit versions 2.0.7 thru 3.0.3. This issue lies in the embedded http server’s parsing of trace requests and may result in denial of service conditions, information disclosure, or remote code execution.
In Fluent Bit 2.1.8 through 2.2.1 a NULL pointer dereference can be caused via an invalid HTTP payload with the content type of x-www-form-urlencoded. It crashes and does not restart. This could result in logs not being delivered properly.
fluent-bit 2.2.2 contains a Use-After-Free vulnerability in /fluent-bit/plugins/customcalyptia/calyptia.c.