Splunk Enterprise CVE-2026-20253: KEV Arbitrary File Creation via PostgreSQL Sidecar

Executive Summary

CISA added CVE-2026-20253 to the Known Exploited Vulnerabilities catalog on 2026-06-18, marking it as actively exploited and requiring vendor mitigations under BOD 26-04 [1]. The affected product is Splunk Enterprise. Splunk’s advisory says an unauthenticated user can create or truncate arbitrary files through a PostgreSQL sidecar service endpoint in Splunk Enterprise 10.2 versions below 10.2.4 and 10 versions below 10.0.7 [2]. NVD corroborates the same ranges, maps the issue to CWE-306, and repeats the vendor mitigation to disable the PostgreSQL sidecar service if upgrading is not immediately possible [3].

This is a new Halting Problems post rather than a duplicate: no existing site post matched the CVE, advisory ID, or Splunk sidecar endpoint selector. The operational priority is filesystem integrity. A successful write primitive on a Splunk host can tamper with configuration, truncate logs, suppress alerts, or damage local files that store secrets or automation state.

Key Facts

CVE: CVE-2026-20253

Vendor: Splunk

Product: Splunk Enterprise

Advisory ID: SVD-2026-0603

Vulnerability Class: Missing authentication for critical function / arbitrary file creation and truncation

CWE: CWE-306

Severity: 9.8 Critical

Affected Versions:

• 10.2 below 10.2.4
• 10 below 10.0.7

Fixed Versions:

• 10.2.4
• 10.0.7
• 10.4.0

KEV Added: 2026-06-18

KEV Due Date: 2026-06-21

Mitigation if upgrade is delayed: disable the PostgreSQL sidecar service in $SPLUNK_HOME/etc/system/local/server.conf with [postgres] disabled = true and restart Splunk Enterprise [2]

Highest Value Evidence:

• $SPLUNK_HOME/etc/system/local/server.conf
• Splunk Enterprise version output
• Splunk audit and access logs
• Filesystem timestamp diffs under Splunk-managed paths

Evidence Assessment

Claim	Status	Evidence
CISA added CVE-2026-20253 to KEV on 2026-06-18 and names Splunk Enterprise as the affected product.	confirmed	The live KEV JSON entry records cveID CVE-2026-20253, vendorProject Splunk, product Enterprise, and dateAdded 2026-06-18 [1].
Splunk says an unauthenticated user can create or truncate arbitrary files through a PostgreSQL sidecar service endpoint.	confirmed	The advisory title and description state exactly that, and the product-status table identifies the affected build ranges [2].
Splunk Enterprise 10.2 below 10.2.4 and 10 below 10.0.7 are affected; 9.4 and earlier are not affected.	confirmed	The advisory solution and product-status sections list those ranges, and NVD mirrors the same version boundaries [2][3].
Splunk recommends upgrading or, if that is not immediate, disabling the PostgreSQL sidecar service.	confirmed	The mitigation section instructs operators to set [postgres] disabled = true in server.conf and restart the instance [2].
Public sources do not publish campaign names, victim counts, hashes, or source IPs.	not observed	The CISA, Splunk, and NVD references used here describe the vulnerability and mitigation path, but none provide those campaign details [1][2][3].

Impact Determination

Classification	Criteria	What to look for	Action
Confirmed compromise	Affected host shows unauthorized file creation/truncation, unexpected Splunk config changes, or log tampering around the sidecar endpoint.	server.conf diffs, timestamp anomalies, audit logs, Splunk process behavior, and restored file comparisons.	Isolate the host, preserve evidence, restore clean files from trusted backups, and rotate any secrets exposed on the host.
Presumed exposed	The instance runs an affected version or version status is unknown, and the PostgreSQL sidecar service remains reachable.	splunkd version output, package inventory, and network exposure evidence.	Patch immediately or disable the PostgreSQL sidecar service using Splunk’s documented workaround.
Potentially exposed	Splunk Enterprise is in inventory but exact version or sidecar configuration is not yet verified.	CMDB, deployment manifests, or direct host inspection.	Inventory the host and verify version plus sidecar status before assuming safety.
Not exposed	The host is on 10.2.4 or later, 10.0.7 or later, or the sidecar service is disabled and validated.	Version proof, negative exposure evidence, and configuration review.	Preserve closure evidence and keep monitoring for tampering attempts.
Unknown	No version evidence or filesystem telemetry is available.	Evidence gap log.	Assume exposure until you can prove otherwise.

Technical Analysis

The vulnerable boundary is not a typical authenticated admin endpoint; it is a network-reachable service component that Splunk’s advisory says lacked authentication controls in affected releases [2]. That matters because file creation and file truncation are enough to damage a host even without direct code execution.

Practical abuse paths include:

• Filesystem integrity loss: overwrite or truncate Splunk configuration, search artifacts, deployment state, or logging data. [2][3]
• Credential exposure: if secrets, tokens, or key material live in readable files on the same host, a file-write primitive can destroy integrity controls or prepare follow-on access by modifying scripts and configs that reference those secrets. [2][3]
• Persistence or tampering: if the process can write into application directories, an attacker may be able to alter startup behavior, suppress detection, or stage a later payload using legitimate Splunk-managed paths. [2][3]

The evidence does not justify claiming specific malware, source IPs, or a particular campaign. It does justify treating affected internet-facing Splunk hosts as high-priority integrity targets because a file-write bug in a management plane can be used to break monitoring, alter configuration, and complicate incident response. [1][2][3]

Downstream Abuse Audits

Filesystem integrity

A file-create/truncate primitive can damage any writable path exposed to the Splunk process. The most immediate defender concern is not remote shell access; it is that an attacker may overwrite or zero out files that Splunk uses for configuration, logging, or local integration state [2][3].

Credential exposure

If the host stores automation credentials, local API tokens, or app-specific secrets under the Splunk install tree or adjacent service directories, those files become part of the blast radius. Even when the vulnerability is only a write primitive, it can still enable credential exposure indirectly by modifying scripts or config that controls how secrets are loaded or protected.

CI/CD and cloud impact

The public evidence here does not show a named CI/CD or cloud-targeting campaign. Still, if a Splunk server participates in deployment automation, holds release credentials, or mirrors logs into a cloud pipeline, file tampering could affect those workflows. Treat that as a conditional downstream risk, not a published fact.

Timeline

• 2026-06-10: Splunk publishes advisory SVD-2026-0603 and the initial disclosure for CVE-2026-20253 [2].
• 2026-06-15: Splunk updates the advisory to add the PostgreSQL disablement workaround [2].
• 2026-06-18: CISA adds CVE-2026-20253 to KEV and sets the due date to 2026-06-21 [1].

Indicators of Compromise

Public source material does not provide hashes, IPs, or malware families for this issue. The following selectors are still useful for local scoping and config review:

Files and Paths

• $SPLUNK_HOME/etc/system/local/server.conf
• server.conf
• [postgres]
• disabled = true

Version Selectors

• 10.2.3
• 10.0.6
• 10.2.4
• 10.0.7

Source and Advisory Selectors

• CVE-2026-20253
• SVD-2026-0603
• https://advisory.splunk.com/advisories/SVD-2026-0603
• https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json

Detection and Hunting

Hunt Manifest: splunk-enterprise-cve-2026-20253-kev-hunt-1

• Title: local repository and telemetry scope
• Question: Does the telemetry scope contain patterns associated with Splunk Enterprise CVE-2026-20253 KEV activity or exposure?
• Telemetry Family: file
• Telemetry Context: host filesystem or log export
• Positive Signal: Indicators matched in telemetry: Splunk CVE-2026-20253 selectors, affected-version strings, or sidecar disablement evidence

#!/usr/bin/env python3
"""Audit Splunk Enterprise CVE-2026-20253 exposure and abuse evidence.

The script scans a repository tree and optional telemetry export tree for
incident-specific selectors drawn from the CISA KEV entry, the Splunk advisory,
and NVD. It reports whether the tree contains version strings, file-path hints,
or mitigation evidence tied to the PostgreSQL sidecar service.
"""

from __future__ import annotations

import json
import os
import sys
from pathlib import Path
from typing import Iterable

CVE_ID = "CVE-2026-20253"
ADVISORY_ID = "SVD-2026-0603"
CISA_FEED_URL = "https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json"
SPLUNK_ADVISORY_URL = "https://advisory.splunk.com/advisories/SVD-2026-0603"
NVD_URL = "https://nvd.nist.gov/vuln/detail/CVE-2026-20253"
DOMAINS = ["www.cisa.gov", "advisory.splunk.com", "nvd.nist.gov"]
PROCESS_PATTERNS = ["splunkd", "postgres"]

AFFECTED_VERSION_STRINGS = [
    "10.2 versions below 10.2.4",
    "10 versions below 10.0.7",
    "10.2.0 to 10.2.3",
    "10.0.0 to 10.0.6",
    "10.2.3",
    "10.0.6",
    "10.2.4",
    "10.0.7",
]
MITIGATION_STRINGS = [
    "[postgres]",
    "disabled = true",
    "$SPLUNK_HOME/etc/system/local/server.conf",
    "disable the PostgreSQL sidecar service",
    "Sidecar Configuration Settings",
    "Postgresql Configuration",
]
CONTEXT_STRINGS = [
    CVE_ID,
    ADVISORY_ID,
    "Splunk Enterprise",
    "PostgreSQL sidecar service endpoint",
    "create or truncate arbitrary files",
]
INDICATORS = sorted({
    *AFFECTED_VERSION_STRINGS,
    *MITIGATION_STRINGS,
    *CONTEXT_STRINGS,
    *DOMAINS,
    *PROCESS_PATTERNS,
    CISA_FEED_URL,
    SPLUNK_ADVISORY_URL,
    NVD_URL,
})
EXCLUDED_DIR_NAMES = {".git", "node_modules", "vendor", "dist", "__pycache__", ".venv"}
TEXT_SUFFIXES = {".conf", ".txt", ".log", ".md", ".json", ".yaml", ".yml", ".py", ".ini", ".cfg", ".xml", ".toml"}


def _scan_tree(root: Path) -> list[dict[str, object]]:
    matches: list[dict[str, object]] = []
    if not root.exists():
        return matches

    for path in root.rglob("*"):
        if path.is_dir():
            continue
        if any(part in EXCLUDED_DIR_NAMES for part in path.parts):
            continue
        if path.suffix and path.suffix not in TEXT_SUFFIXES and path.name not in {"server.conf"}:
            # Keep the scan focused on text-like files, but still allow key config names.
            continue
        try:
            content = path.read_text(errors="ignore")
        except Exception:
            continue
        hits = [indicator for indicator in INDICATORS if indicator.lower() in content.lower()]
        if hits:
            matches.append({
                "path": str(path),
                "hits": sorted(set(hits)),
            })
    return matches


def _ensure_out_dir(out_dir: Path) -> None:
    out_dir.mkdir(parents=True, exist_ok=True)


def _write_lines(path: Path, lines: Iterable[str]) -> None:
    path.write_text("\n".join(lines) + "\n", encoding="utf-8")


def main() -> int:
    root = Path(sys.argv[1]) if len(sys.argv) > 1 else Path(".")
    log_root_env = os.environ.get("LOG_ROOT", "").strip()
    log_root = Path(log_root_env) if log_root_env else None
    out_dir = Path(os.environ.get("OUT", "hp-splunk-enterprise-cve-2026-20253-kev-scope"))
    _ensure_out_dir(out_dir)

    selectors_file = out_dir / "selectors.txt"
    _write_lines(selectors_file, INDICATORS)

    repo_matches = _scan_tree(root)
    log_matches = _scan_tree(log_root) if log_root else []

    report = {
        "cve_id": CVE_ID,
        "advisory_id": ADVISORY_ID,
        "root": str(root),
        "log_root": str(log_root) if log_root else "",
        "indicator_count": len(INDICATORS),
        "repository_matches": repo_matches,
        "telemetry_matches": log_matches,
        "exposure_signals": {
            "affected_version_seen": any(
                any(version.lower() in hit.lower() for hit in entry["hits"])  # type: ignore[index]
                for entry in repo_matches
                for version in AFFECTED_VERSION_STRINGS
            ),
            "mitigation_seen": any(
                any(mitig.lower() in hit.lower() for hit in entry["hits"])  # type: ignore[index]
                for entry in repo_matches
                for mitig in MITIGATION_STRINGS
            ),
        },
    }

    report_path = out_dir / "audit-report.json"
    report_path.write_text(json.dumps(report, indent=2, sort_keys=True) + "\n", encoding="utf-8")

    summary = [
        f"[+] selectors written: {selectors_file}",
        f"[+] repository matches: {len(repo_matches)}",
        f"[+] telemetry matches: {len(log_matches)}",
        f"[+] report written: {report_path}",
    ]
    print("\n".join(summary))
    return 0


if __name__ == "__main__":
    raise SystemExit(main())

Remediation and Closure

1. Upgrade Splunk Enterprise to 10.2.4, 10.0.7, or 10.4.0 or later [2].
2. If you cannot upgrade immediately, disable the PostgreSQL sidecar service as Splunk documents and restart the instance [2].
3. Verify that Splunk-managed files under $SPLUNK_HOME/etc/system/local/ and adjacent app directories have not been truncated or replaced.
4. Preserve file hashes, timestamps, and relevant logs before restoring any affected configuration.
5. Keep the incident open until version proof, mitigation proof, and a negative integrity review are all complete.

Sources

1. CISA Known Exploited Vulnerabilities catalog JSON
2. Splunk advisory SVD-2026-0603
3. NVD CVE-2026-20253