EUVD-2025-198811

Comprehensive Technical Analysis of EUVD-2025-198811

1. Vulnerability Assessment and Severity Evaluation

The vulnerability described in EUVD-2025-198811 affects Fluent Bit, a popular open-source log processor and forwarder. Specifically, the in_http, in_splunk, and in_elasticsearch input plugins fail to properly sanitize tag_key inputs. This oversight allows attackers to inject special characters such as newlines or path traversal sequences (../), which are then treated as valid tags. The severity of this vulnerability is rated with a CVSS Base Score of 9.1, indicating a critical issue.

CVSS Vector Breakdown:

• AV:N (Network Vector): The vulnerability is exploitable over the network.
• AC:L (Low Complexity): The attack requires low skill or resources.
• PR:N (No Privileges Required): No special privileges are needed to exploit the vulnerability.
• UI:N (No User Interaction): No user interaction is required.
• S:U (Unchanged): The scope of the vulnerability does not change.
• C:H (High Confidentiality Impact): The vulnerability can lead to significant data disclosure.
• I:H (High Integrity Impact): The vulnerability can lead to significant data alteration.
• A:N (No Availability Impact): The vulnerability does not directly impact system availability.

2. Potential Attack Vectors and Exploitation Methods

• Newline Injection: Attackers can inject newlines into tag_key values, potentially altering log entries and causing misrouting of logs.
• Path Traversal: By injecting ../ sequences, attackers can manipulate file paths, leading to unauthorized access to files or directories.
• Forged Record Injection: Attackers can inject forged records into the log stream, compromising data integrity.
• Log Misrouting: Manipulating tag_key values can misroute logs, affecting log analysis and monitoring systems.

3. Affected Systems and Software Versions

The vulnerability affects Fluent Bit version 4.1.0. It is crucial to note that other versions might also be affected if they share the same input plugins and lack proper sanitization mechanisms.

4. Recommended Mitigation Strategies

• Update Software: Immediately update to the latest version of Fluent Bit that includes a fix for this vulnerability.
• Input Validation: Implement additional input validation and sanitization mechanisms to ensure that tag_key values do not contain special characters.
• Network Segmentation: Segment networks to limit access to Fluent Bit instances, reducing the attack surface.
• Monitoring and Logging: Enhance monitoring and logging to detect and respond to suspicious activities related to log processing and routing.
• Access Controls: Implement strict access controls to limit who can write records into Splunk or Elasticsearch.

5. Impact on European Cybersecurity Landscape

This vulnerability poses a significant risk to organizations relying on Fluent Bit for log processing and forwarding. Given the widespread use of Fluent Bit in various industries, including finance, healthcare, and government, the potential impact on data integrity and log routing could be substantial. Organizations must prioritize patching and implementing robust security measures to mitigate this risk.

6. Technical Details for Security Professionals

• Vulnerability Identification: The vulnerability is identified as CVE-2025-12977 and is assigned by certcc.
• References:
  • Fluent Bit Announcement: Fluent Bit v4.1.0 Announcement
  • NVD Entry: CVE-2025-12977
• ENISA IDs:
  • Product: 24f6adf3-ce78-3472-ba6d-f7a26d950590 (FluentBit v4.1.0)
  • Vendor: 68bc6891-8dae-3c32-9535-6e52c3ae9e16 (FluentBit)

Conclusion:

The vulnerability in Fluent Bit's input plugins poses a critical risk to data integrity and log routing. Organizations must act swiftly to update their software and implement additional security measures to protect against potential exploitation. Continuous monitoring and proactive security practices are essential to mitigate such risks effectively.