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CVE-2025-12978 is a tag-matching flaw in Fluent Bit affecting the in_http, in_splunk, and in_elasticsearch input plugins. The vulnerability is in the tag_key validation/matching logic, which fails to enforce exact key-length matching and instead performs a partial string comparison. As described in the provided content, a crafted input can cause a tag prefix to be treated as a full match, allowing an attacker to spoof a trusted tag by guessing only the first character of the configured Tag_Key. This can cause attacker-supplied records to be assigned unintended tags and routed as if they originated from trusted sources.
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An input validation weakness in Fluent Bit’s tag_key record processing that can enable unsafe tag values, potentially leading to downstream path traversal/injection/unexpected writes depending on outputs and configuration.
A tag-matching logic weakness in Fluent Bit that allows spoofing of trusted tags by guessing only the first character of a Tag_Key, enabling log rerouting, filter bypass, and injection of misleading/malicious records.
Partial string comparison in tag_key() allows matching Tag_Key using only attacker-supplied prefix (e.g., first character), enabling tag spoofing and log routing/filter bypass.
A tag-spoofing weakness in Fluent Bit inputs (HTTP, Elasticsearch, Splunk) enabling attackers to spoof trusted tags, potentially causing log rerouting, filter bypass, and malicious record injection.
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