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.

fluent-bit 2.2.2 contains a Use-After-Free vulnerability in /fluent-bit/plugins/customcalyptia/calyptia.c.

Summary

Treasure Data's digdag workload automation system is susceptible to a path traversal vulnerability if it's configured to store log files locally.

Impact

This issue may lead to Information Disclosure.

An issue was discovered in Fluent Bit 3.1.9. When the OpenTelemetry 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 processpayloadtracesprotong() at opentelemetryprot.c.

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.

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.

CVE-2025-12969

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-2025-12970

Fluent Bit outfile plugin does not properly sanitize tag values when deriving output file names. When the File option is omitted, the plugin uses untrusted tag input to construct file paths. This allows attackers with network access to craft tags containing path traversal sequences that cause Fluent Bit to write files outside the intended output directory.

CVE-2025-12977

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 Treasure Data Fluent Bit 1.7.1, erroneous parsing in flbpackmsgpacktojsonformat leads to type confusion bug that interprets whatever is on the stack as msgpack maps and arrays, leading to use-after-free. This can be used by an attacker to craft a specially craft file and trick the victim opening it using the affect software, triggering use-after-free and execute arbitrary code on the target system.

An issue was discovered in Treasure Data Fluent Bit 1.7.1, a wrong variable is used to get the msgpack data resulting in a heap overflow in flbmsgpackgelfvalueext. An attacker can craft a malicious file and tick the victim to open the file with the software, triggering a heap overflow and execute arbitrary code on the target system.

An issue was discovered in the MQTT input plugin in Fluent Bit through 1.0.4. When this plugin acts as an MQTT broker (server), it mishandles incoming network messages. After processing a crafted packet, the plugin's mqttpacketdrop function (in /plugins/inmqtt/mqttprot.c) executes the memmove() function with a negative size parameter. That leads to a crash of the whole Fluent Bit server via a SIGSEGV signal.

flbgzipcompress in flbgzip.c in Fluent Bit before 1.6.4 has an out-of-bounds write because it does not use the correct calculation of the maximum gzip data-size expansion.

Fluent Bit (aka fluent-bit) 1.7.0 through 1.7,4 has a double free in flbfree (called from flbparserjsondo and flbparserdo).

Fluent Bit 1.6.10 has a NULL pointer dereference when an flbmalloc return value is not validated by flbavro.c or httpserver/api/v1/metrics.c.