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SplunkApplication

CVE-2021-31559

HIGH · 7.5 CVSS v3.1 Published 2022-05-06
Fix available
A fix is available. Upgrade to 8.1.5 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A crafted request bypasses S2S TCP Token authentication writing arbitrary events to an index in Splunk Enterprise Indexer 8.1 versions before 8.1.5 and 8.2 versions before 8.2.1. The vulnerability impacts Indexers configured to use TCPTokens. It does not impact Universal Forwarders.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A crafted HTTP request bypasses S2S (Splunk-to-Splunk) TCP Token authentication in Splunk Enterprise Indexers, allowing an attacker to write arbitrary events to any index. The vulnerability affects Indexers configured with TCPTokens but does not impact Universal Forwarders.

MitigationUpgrade Splunk Enterprise to version 8.1.5 or later (for 8.1.x) or 8.2.1 or later (for 8.2.x) to remediate this authentication bypass vulnerability.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
SplunkApplication
Affected:>= 8.1.0, < 8.1.5= 8.2.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Confirm Splunk product type is Enterprise Indexer
    Run 'splunk --version' or check $SPLUNK_HOME/etc/splunk-launch.conf to identify if this is Splunk Enterprise or Universal Forwarder. Indexers are affected; Universal Forwarders are not.
    Affected if The installed product is a Universal Forwarder (in which case the system is NOT affected)
  2. Determine the installed Splunk Enterprise version
    Run 'splunk --version' or inspect $SPLUNK_HOME/etc/splunk-buildinfo to read the exact version number.
    Affected if Version is 8.1.0 through 8.1.4, or exactly 8.2.0
  3. Verify this is an Indexer with S2S TCPTokens configured
    Check $SPLUNK_HOME/etc/system/local/inputs.conf (or default/inputs.conf) for [tcp-ssl:] or [tcp:] stanzas containing a 'token=' parameter. Alternatively, query the Splunk REST endpoint /services/server/introspection/actor to confirm the server role is 'indexer'.
    Affected if This is NOT an Indexer, or no TCPTokens are configured (the system is NOT affected)
  4. Confirm the S2S receiver is enabled
    Check $SPLUNK_HOME/etc/system/local/server.conf for [general] enableSplunkWebSSL=1 and verify the receiving port is active via 'splunk show web-port' or by inspecting the listening ports on the system.
    Affected if The S2S receiver is not enabled and no TCPToken input listeners are active

The environment is affected only if this is a Splunk Enterprise Indexer (not Universal Forwarder) running version 8.1.0-8.1.4 or exactly 8.2.0, with S2S TCPTokens configured and the receiver enabled.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 8.1.5 or later
Fixed in 8.1.5
Interim mitigation

Upgrade Splunk Enterprise to version 8.1.5 or later (for 8.1.x) or 8.2.1 or later (for 8.2.x) to remediate this authentication bypass vulnerability.

Recommended fix High confidence

Splunk Enterprise 8.1.5 or 8.2.1 (or later stable releases)

  1. 1. Identify the current Splunk Enterprise Indexer version using the 'splunk version' command or the web interface (Settings > Server settings > Server info)
  2. 2. For versions 8.1.0-8.1.4: Plan upgrade to Splunk Enterprise 8.1.5 or later
  3. 3. For version 8.2.0: Plan upgrade to Splunk Enterprise 8.2.1 or later
  4. 4. Review Splunk upgrade documentation and create a backup of your configuration
  5. 5. Download the appropriate fixed version from splunk.com
  6. 6. Perform the upgrade during a planned maintenance window
  7. 7. After upgrade, verify S2S TCP Token authentication is functioning correctly
  8. 8. Confirm the vulnerability is resolved by testing that unauthorized requests without valid tokens are rejected
Caveat Standard Splunk minor version upgrades typically maintain configuration compatibility; however, always review release notes for any changes to indexing, authentication, or forwarding behavior before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Splunk Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,420
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-31559 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data