Telemetry and log collection are core pillars of cloud observability — but newly discovered vulnerabilities in the open-source log processor Fluent Bit introduce serious security risks. These flaws can be chained by attackers to execute remote code, corrupt logs, bypass authentication, and infiltrate cloud environments or Kubernetes clusters undetected.
Summary of the New Fluent Bit Vulnerabilities
Security researchers recently identified five critical vulnerabilities in Fluent Bit:
1. CVE-2025-12972 – Path Traversal (out_file plugin)
A flaw in the file output plugin allows attackers to write or overwrite arbitrary files using malicious tag values. This can lead to log corruption, file deletion, or privilege escalation.
2. CVE-2025-12970 – Stack Buffer Overflow (in_docker plugin)
A specially crafted container name can trigger a buffer overflow, potentially resulting in remote code execution or system crashes.
3. CVE-2025-12978 – Tag Spoofing & Routing Manipulation
Attackers can guess the first character of a tag and then spoof trusted tags, allowing them to inject logs, reroute traffic, or hide their activity inside legitimate log streams.
4. CVE-2025-12977 – Input Sanitization Failure
Tags sourced from user input are not properly sanitized, which enables path traversal, newline injection, or the insertion of control characters.
5. CVE-2025-12969 – Missing Authentication (in_forward plugin)
A critical design oversight allows attackers to send logs or telemetry data without authentication, opening the door to log tampering or data injection.
Why These Flaws Matter for Cloud & Kubernetes Security
These vulnerabilities pose a serious risk because:
- Fluent Bit is widely deployed, especially as a DaemonSet in Kubernetes clusters.
- Exploitation requires low skill — some attacks only need basic knowledge of tags.
- Attackers can become invisible by corrupting, overwriting, or injecting false logs.
- Node takeover is possible since compromised log agents often run with high privileges.
- Affects multi-cloud environments that rely heavily on Fluent Bit for observability.
This makes the vulnerabilities extremely attractive for attackers looking to hide activity, escalate privileges, or launch stealthy supply-chain style intrusions.
Not the First Time: Fluent Bit Has a History of Severe Bugs
In 2024, another major vulnerability — widely known as the “Linguistic Lumberjack” bug — affected several earlier versions of Fluent Bit. That flaw permitted memory corruption, denial-of-service, and potential code execution.
The new flaws demonstrate an ongoing pattern: even trusted log agents can become high-impact attack vectors.
How Organizations Should Respond Immediately
1. Upgrade to Patched Versions
The vulnerabilities are fixed in the latest Fluent Bit releases. Immediate upgrade is strongly recommended.
2. Avoid Dynamic or Untrusted Tags
Use static, controlled tag values to prevent tag spoofing or path traversal attacks.
3. Restrict Output Paths
Ensure the file output plugin writes only to locked-down directories. Never derive file names from untrusted tags.
4. Enforce Read-Only Configurations
Mount Fluent Bit config directories as read-only to prevent runtime tampering.
5. Apply Least Privilege
Run Fluent Bit as a non-root user and minimize filesystem or network permissions.
6. Limit Network Exposure
Lock down the in_forward plugin to trusted sources only.
A Wake-Up Call for Cloud & DevSecOps Teams
This incident highlights a critical truth: your logging infrastructure is part of your attack surface.
If attackers can manipulate logs:
- They can erase their tracks
- They can mislead detection tools
- They can maintain persistent access
- They can sabotage audit trails and compliance reports
As cloud environments grow more complex, securing the observability pipeline is just as important as securing applications themselves.
Final Thoughts
The new Fluent Bit flaws reinforce the need for continuous hardening, rapid patching, and proactive monitoring. Cloud and Kubernetes teams must treat log agents as sensitive components that require the same security scrutiny as any other workload.
