CriticalCVE-2026-20253

    Splunk Enterprise Missing Authentication for Critical Function Vulnerability (CVE-2026-20253)

    Published Last modified In CISA KEV since Sources: CVE.org, BSI

    What is affected, what to do

    In Splunk Enterprise 10.2 versions below 10.2.4 and 10 versions below 10.0.7, an unauthenticated user could create or truncate arbitrary files through a PostgreSQL sidecar service endpoint. The vulnerability exists because the PostgreSQL sidecar service endpoint lacks authentication controls, allowing any network-reachable user to invoke file operations without credentials.

    The vulnerability is being actively exploited; treat it as a priority. Update Splunk Enterprise to version 10.2.4, Splunk Enterprise to version 10.0.7. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Splunk Enterprise lt 10.2..10.2.4
    • Splunk Enterprise lt 10.0..10.0.7
    Fixed in
    • Splunk Enterprise 10.2.4
    • Splunk Enterprise 10.0.7

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.8

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: CVE.org, BSI

    96.9 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.89

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    247.62 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.8 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.8
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    96.9 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.89
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-306

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is network-reachable without authentication or user interaction and sits among the CVEs most likely to be exploited. Exploitation is trivial because the endpoint simply has no access control. CISA does not flag ransomware use, but the real risk is that Splunk is frequently the organisation's central SIEM: an attacker able to create or truncate files can sabotage detection and evidence, disrupt operations and potentially stage further persistence. NIS2/KRITIS organisations running Splunk 10.0 or 10.2 should treat this as an emergency change within 24 hours, and as a likely security incident if the sidecar endpoint was reachable from user or external networks; estates on 9.4 or earlier need no action for this CVE.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Scope the estate: Enumerate every Splunk Enterprise instance (search heads, indexers, heavy forwarders, deployment server, cluster manager) and check its version ($SPLUNK_HOME/bin/splunk version). Only the 10.2.x below 10.2.4 and 10.0.x below 10.0.7 branches are affected. The vendor states 9.4 and earlier are not affected.
      • Patch: Upgrade affected instances to 10.2.4 or 10.0.7. Prioritise nodes whose network interfaces are reachable from user VLANs, the DMZ or the internet.
      • If you cannot upgrade today: Disable the PostgreSQL sidecar service. This is the vendor-documented workaround; follow the Splunk advisory for the exact procedure. Restart Splunk, then confirm the sidecar process is gone and its listeners are closed (ss -tlnp, or Get-NetTCPConnection -State Listen on Windows).
      • Cut exposure now: Restrict the sidecar's listening ports to localhost or Splunk cluster peers via host firewall or perimeter ACL. Identify the actual port on the host rather than assuming one.
      • Check integrity: Hunt for unexpected new files or files truncated to 0 bytes. Focus on $SPLUNK_HOME/etc/ (configs, passwd, apps), index directories and OS files. Splunk is often the SIEM itself, so an attacker can wipe the evidence and blind detection.
      • If compromise is suspected: Isolate the host and take a forensic image. Before restoring from a known-good backup, rotate Splunk admin credentials, HEC tokens and service-account passwords.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Place Splunk management interfaces and sidecar endpoints in a dedicated management VLAN. Allow access only from designated admin jump hosts and between cluster nodes, with default deny. Allow no direct internet reachability.
      • Host firewall: On every Splunk node, drop inbound traffic to the sidecar listener from anything other than 127.0.0.1, using iptables/nftables or a per-port Windows Firewall rule. This provides a protective layer even if patching slips.
      • IPS/NDR: Write a Suricata or Zeek rule that alerts on any TCP session to the sidecar port from a source outside the Splunk node list. In a properly segmented environment, every hit is an alert. Deploy vendor IPS signatures as they ship.
      • Filesystem hardening: Keep write permissions for the Splunk service account to the minimum required, and never run Splunk as root/SYSTEM. This limits how far arbitrary file operations can reach into system paths.
      • Resilience: Keep immutable backups of $SPLUNK_HOME/etc and critical indexes. Dual-forward security-relevant logs to a second destination so truncation on an indexer does not mean total loss.

    3. Runbook step 3

      Detection rules

      • Linux auditd: -w /opt/splunk/etc -p wa -k splunk_cfg, plus monitoring of O_TRUNC/creat syscalls where exe matches the PostgreSQL sidecar binary. Alert on any write outside its own data directory.
      • Sysmon (Windows): EID 11 (FileCreate) where Image is the PostgreSQL process under $SPLUNK_HOME and TargetFilename is outside the Postgres data path. Use EID 3 to catch inbound network connections to that process from non-local IPs.
      • Network telemetry (Zeek): conn.log where id.resp_p == <sidecar port> and id.orig_h not in splunk_nodes → alert. Escalate port scans targeting Splunk hosts.
      • Splunk self-monitoring: Search index=_internal for config- or index-file load errors and sudden ingestion gaps, e.g. | tstats count where index=* by _time span=5m, index with anomaly detection on abrupt drops. Truncated files typically surface as parse or startup errors.
      • File integrity (FIM/EDR): Alert on 0-byte files under $SPLUNK_HOME/etc or /etc. Also alert on new files in app directories (etc/apps/*/bin, default/, local/) that do not map to a change ticket.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    In Splunk Enterprise 10.2 versions below 10.2.4 and 10 versions below 10.0.7, an unauthenticated user could create or truncate arbitrary files through a PostgreSQL sidecar service endpoint. The vulnerability exists because the PostgreSQL sidecar service endpoint lacks authentication controls, allowing any network-reachable user to invoke file operations without credentials. Splunk Enterprise versions 9.4 and earlier are not affected. If you cannot immediately upgrade to a fixed version, you can mitigate this vulnerability by disabling the PostgreSQL sidecar service.

    Source: CISA KEV Catalog, NVD (NIST), CVE.org (MITRE), cvelistv5, BSI WID Portal, BSI CSAF

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    SplunkSplunk Enterprise
    • 10.0 – < 10.0.7
    • 10.2 – < 10.2.4
    • < 10.0.7
    • < 10.2.4
    • < 9.4.12
    • < 9.3.13
    • 10.0.7
    • 10.2.4
    • 10.0.7
    • 10.2.4
    • 9.4.12
    • 9.3.13
    splunksplunk
    • 10.0.0 – < 10.0.7
    • 10.2.0 – < 10.2.4
    • 10.0.7
    • 10.2.4

    Vendors and products

    Weakness classes (CWE)

    • CWE-306Missing Authentication for Critical Function

      Base

      The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.

      Entry at MITRE CWE-306

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    Reference tagged as exploitlabs.watchtowr.com (opens in a new tab)PoC (publicly reported)reported, not verified—
    PoC-in-GitHub (nomi-sec)CVE-2026-20253-Splunk-Enterprise-Pre-Auth-RCE- (opens in a new tab)github.comPoC (publicly reported)reported, not verified
    PoC-in-GitHub (nomi-sec)CVE-2026-20253 (opens in a new tab)github.comPoC (publicly reported)reported, not verified
    PoC-in-GitHub (nomi-sec)CVE-2026-20253 (opens in a new tab)github.comPoC (publicly reported)reported, not verified
    PoC-in-GitHub (nomi-sec)CVE-2026-20253 (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    References & sources

    • advisory.splunk.comadvisories/SVD-2026-0603
    • labs.watchtowr.comwhy-use-app-level-auth-when-every-database-has-auth-splunk-ente…Exploit
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2026-20253government-resource

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. NVD analysis modifiedNVD

      Show 3 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Reference typechanged
      Cisco Systems, Inc.: https://advisory.splunk.com/advisories/SVD-2026-0603 Types: Vendor Advisory
      Cisco Systems, Inc.: https://advisory.splunk.com/advisories/SVD-2026-0603 Types: Mitigation, Vendor Advisory
      Reference typeadded
      —
      CISA-ADP: https://labs.watchtowr.com/why-use-app-level-auth-when-every-database-has-auth-splunk-enterprise-cve-2026-20253-pre-auth-rce/ Types: Exploit, Third Party Advisory
      Reference typeadded
      —
      CISA-ADP: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-20253 Types: US Government Resource

      Source identifier: nvd@nist.gov

    2. Record modifiedCISA ADP

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://labs.watchtowr.com/why-use-app-level-auth-when-every-database-has-auth-splunk-enterprise-cve-2026-20253-pre-auth-rce/

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    3. Record modifiedCisco

      Description added or changed

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionchanged
      In Splunk Enterprise versions below 10.2.4 and 10.0.7, an unauthenticated user could create or truncate arbitrary files through a PostgreSQL sidecar service endpoint.<br><br>The vulnerability exists because the PostgreSQL sidecar service endpoint lacks authentication controls, allowing any network-reachable user to invoke file operations without credentials.
      In Splunk Enterprise 10.2 versions below 10.2.4 and 10 versions below 10.0.7, an unauthenticated user could create or truncate arbitrary files through a PostgreSQL sidecar service endpoint. The vulnerability exists because the PostgreSQL sidecar service endpoint lacks authentication controls, allowing any network-reachable user to invoke file operations without credentials. Splunk Enterprise versions 9.4 and earlier are not affected. If you cannot immediately upgrade to a fixed version, you can mitigate this vulnerability by disabling the PostgreSQL sidecar service.

      Source identifier: psirt@cisco.com

    4. Record modifiedCisco

      Description added or changed

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionchanged
      In Splunk Enterprise versions below 10.2.4 and 10.0.7, and Splunk Cloud Platform versions below 10.4.2604.3 and 10.2.2510.14, an unauthenticated user could create or truncate arbitrary files through a PostgreSQL sidecar service endpoint.<br><br>The vulnerability exists because the PostgreSQL sidecar service endpoint lacks authentication controls, allowing any network-reachable user to invoke file operations without credentials.
      In Splunk Enterprise versions below 10.2.4 and 10.0.7, an unauthenticated user could create or truncate arbitrary files through a PostgreSQL sidecar service endpoint.<br><br>The vulnerability exists because the PostgreSQL sidecar service endpoint lacks authentication controls, allowing any network-reachable user to invoke file operations without credentials.

      Source identifier: psirt@cisco.com

    5. Initial analysis by NVDNVD

      Newly listed as affected:
      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Product configurationadded
      —
      OR *cpe:2.3:a:splunk:splunk:*:*:*:*:enterprise:*:*:* versions from (including) 10.0.0 up to (excluding) 10.0.7 *cpe:2.3:a:splunk:splunk:*:*:*:*:enterprise:*:*:* versions from (including) 10.2.0 up to (excluding) 10.2.4
      Reference typeadded
      —
      Cisco Systems, Inc.: https://advisory.splunk.com/advisories/SVD-2026-0603 Types: Vendor Advisory

      Source identifier: nvd@nist.gov

    Show one older change

    1. ReceivedCisco

      CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

      Weakness type: CWE-306

      Description added or changed

      Show 4 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      In Splunk Enterprise versions below 10.2.4 and 10.0.7, and Splunk Cloud Platform versions below 10.4.2604.3 and 10.2.2510.14, an unauthenticated user could create or truncate arbitrary files through a PostgreSQL sidecar service endpoint.<br><br>The vulnerability exists because the PostgreSQL sidecar service endpoint lacks authentication controls, allowing any network-reachable user to invoke file operations without credentials.
      CVSSadded
      —
      AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
      Weakness type (CWE)added
      —
      CWE-306
      Referenceadded
      —
      https://advisory.splunk.com/advisories/SVD-2026-0603

      Source identifier: psirt@cisco.com

    One NVD translation into another language is hidden.

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