CVE-2025-12972
MediumCVSS 5.3Exploitation Probability (EPSS)
Elevated risk58th percentile - higher than 58% of all known CVEs
Summary
Fluent Bit out_file 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.
Risk Assessment
An attacker could write files to arbitrary locations on the server, potentially overwriting system files or placing malware.
Recommendation
Upgrade Fluent Bit to a patched version and avoid omitting the File option in configuration.
Other vulnerabilities in Fluent Bit
See all- CVE-2026-61674Critical
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.
- CVE-2025-12977Critical
Fluent Bit input plugins (in_http, in_splunk, in_elasticsearch) fail to sanitize tag_key inputs. An attacker with network access or the ability to write records into Splunk or Elasticsearch can supply tag_key values containing special characters like newlines or ../ that are treated as valid tags.
- CVE-2025-12978Medium
Fluent Bit in_http, in_splunk, and in_elasticsearch input plugins contain a flaw in tag_key validation logic that fails to enforce exact key-length matching. This allows an attacker with access to these endpoints to manipulate tags and redirect records to unintended destinations. This can lead to injection of forged data and routing manipulation.
- CVE-2025-12969Medium
The in_forward input plugin in Fluent Bit does not properly enforce the security.users authentication mechanism under certain configuration conditions. Remote attackers with network access to the Fluent Bit instance exposing the forward input can send unauthenticated data.
Original NVD description (English source)
Fluent Bit out_file 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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS