CVE-2025-12977: fluentbit fluent bit

Vulnerability summary

CVE-2025-12977 is a critical (CVSS 9.1) vulnerability in fluentbit fluent bit. EPSS estimates a 0.73% chance of exploitation in the next 30 days, higher than 53.4% of scored vulnerabilities.

Timeline

1. 24-11-2025
   PublishedVulnerability first disclosed.
2. 07-01-2026
   Last modifiedVulnerability information updated.

Description

Fluent Bit in_http, in_splunk, and in_elasticsearch input plugins 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 such as newlines or ../ that are treated as valid tags. Because tags influence routing and some outputs derive filenames or contents from tags, this can allow newline injection, path traversal, forged record injection, or log misrouting, impacting data integrity and log routing.

• CWE-1287Improper Validation of Specified Type of InputThe product receives input that is expected to be of a certain type, but it does not validate or incorrectly validates that the input is actually of the expected type.