How to Fix CVE-2026-20205: Information written to log files can in Splunk MCP Server

By Sai Kiran Pandrala. Last verified: 2026-05-25.

What is CVE-2026-20205?

In Splunk MCP Server app versions below 1.0.3, a user who holds a role with access to the Splunk _internal index or possesses the high-privilege capability mcp_tool_admin could view users session and authorization tokens in clear text.<br><br>The vulnerability would require either local access to the log files or administrative access to internal indexes, which by default only the admin role receives. <br><br>Review roles and capabilities on your instance and restrict internal index access to administrator-level roles. See Define roles on the Splunk platform with capabilities and Connecting to MCP Server and Admin settings in the Splunk documentation for more information.

Am I affected?

Run the version check that matches your platform:

# Linux
dpkg -s splunk 2>/dev/null | grep -i version
rpm -q splunk 2>/dev/null
splunk --version 2>/dev/null

Compare what you see against the Affected row above (Splunk 1.0 to <1.0.3). If your build sits inside that range, you are exposed and should patch.

How to fix CVE-2026-20205

The primary fix is to upgrade Splunk MCP Server to the patched build. Use the commands for your platform below; the patched version listed in the vendor advisory is: Splunk MCP Server 1.0.3.

Ubuntu / Debian

sudo apt-get update
sudo apt-get install --only-upgrade splunk
splunk --version 2>/dev/null || dpkg -s splunk | grep -i version

RHEL / CentOS / Rocky / AlmaLinux

sudo dnf upgrade --security splunk -y
rpm -q splunk

SUSE / openSUSE

sudo zypper patch --category security
rpm -q splunk

Complete PowerShell remediation script (Windows)

# Fix script for CVE-2026-20205 affecting Splunk MCP Server
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2026-20205-fix-$(Get-Date -Format yyyyMMdd-HHmmss).log"
New-Item -ItemType Directory -Force (Split-Path $LogPath) | Out-Null
Start-Transcript -Path $LogPath -Append

try {
    Write-Host "[1/4] Detecting installed version of Splunk MCP Server"
    $pkg = winget list --id "Splunk_MCP_Server" 2>$null
    Write-Host $pkg

    Write-Host "[2/4] Backing up configuration"
    $backup = "C:\Backup\Splunk_MCP_Server-$(Get-Date -Format yyyyMMdd)"
    New-Item -ItemType Directory -Force $backup | Out-Null
    Get-ChildItem "C:\ProgramData\Splunk_MCP_Server" -ErrorAction SilentlyContinue |
        Copy-Item -Destination $backup -Recurse -Force -ErrorAction SilentlyContinue

    Write-Host "[3/4] Applying upgrade to Splunk MCP Server 1.0.3"
    winget upgrade --id "Splunk_MCP_Server" --silent --accept-source-agreements --accept-package-agreements
    # Fallback: Windows Update for OS-level fixes
    if ($LASTEXITCODE -ne 0) {
        Install-Module -Name PSWindowsUpdate -Force -SkipPublisherCheck -ErrorAction SilentlyContinue
        Import-Module PSWindowsUpdate
        Install-WindowsUpdate -MicrosoftUpdate -AcceptAll -IgnoreReboot
    }

    Write-Host "[4/4] Verifying patched build"
    winget list --id "Splunk_MCP_Server"
    Write-Host "Fix applied. Reboot if prompted."
    exit 0
} catch {
    Write-Error "Patch failed: $_"
    exit 1
} finally {
    Stop-Transcript
}

Complete Bash remediation script (Linux)

#!/usr/bin/env bash
# Fix script for CVE-2026-20205 affecting Splunk MCP Server
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2026-20205-fix-$(date +%Y%m%d-%H%M%S).log"
exec > >(tee -a "$LOG") 2>&1

echo "[1/4] Detecting installed version"
if command -v dpkg >/dev/null; then
    dpkg -s splunk 2>/dev/null | grep -i version || echo "splunk not installed via dpkg"
elif command -v rpm >/dev/null; then
    rpm -q splunk || echo "splunk not installed via rpm"
fi

echo "[2/4] Backing up configuration"
BACKUP="/root/backup-cve-2026-20205-$(date +%Y%m%d)"
mkdir -p "$BACKUP"
for d in /etc/splunk /etc/splunk.d /etc/splunk.conf; do
    [ -e "$d" ] && cp -a "$d" "$BACKUP/" || true
done

echo "[3/4] Applying upgrade (target: Splunk MCP Server 1.0.3)"
if command -v apt-get >/dev/null; then
    apt-get update
    apt-get install --only-upgrade -y splunk
elif command -v dnf >/dev/null; then
    dnf upgrade --security -y splunk
elif command -v yum >/dev/null; then
    yum update -y splunk
elif command -v zypper >/dev/null; then
    zypper --non-interactive patch --category security
fi

echo "[4/4] Verifying patched build"
if command -v dpkg >/dev/null; then
    dpkg -s splunk 2>/dev/null | grep -i version
elif command -v rpm >/dev/null; then
    rpm -q splunk
fi
echo "Done. Restart any running daemons that loaded the old library."

If you can't patch immediately

If you cannot apply the patched version today, restrict exposure with one of the following runnable controls. None replace the patch.

Network restriction (Linux, nftables)

# Block inbound traffic to the affected service from untrusted networks
sudo nft add table inet filter
sudo nft 'add chain inet filter input { type filter hook input priority 0 ; }'
sudo nft 'add rule inet filter input tcp dport {443, 80} ip saddr != 10.0.0.0/8 drop'
sudo nft list ruleset

Service-level fallback

# If the affected feature is optional, stop the service until the patch is applied
sudo systemctl stop splunk
sudo systemctl disable splunk

How to verify the fix worked

# Linux
splunk --version 2>/dev/null || dpkg -s splunk | grep -i version
rpm -q splunk 2>/dev/null || true

# Windows
winget list | findstr /I "splunk"
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

Expected: the reported version is at or above Splunk MCP Server 1.0.3. Restart any services that loaded the old library (systemctl restart <service> on Linux, restart the Windows service or reboot when prompted). For network appliances, run show version on the device and confirm the build matches the patched release.

Frequently asked questions

Related fixes

Other vulnerabilities in the same area that are worth patching alongside this one:

• How to Fix CVE-2026-3463: Heap buffer overflow in xlnt — Heap buffer overflow in xlnt
• How to Fix CVE-2026-24990: Critical Vulnerability in WP Docs — Critical Vulnerability in WP Docs
• How to Fix CVE-2026-1568: Authentication Bypass in Vulnerability Management , Authentication Bypass in Vulnerability Management
• How to Fix CVE-2026-32623: Heap buffer overflow in xrdp , Heap buffer overflow in xrdp
• How to Fix CVE-2026-7098: Buffer Overflow in F456 , Buffer Overflow in F456

Is CVE-2026-20205 actually being exploited?

According to the data sources above, no public confirmation of in-the-wild exploitation at this time. Either way, the fix is the same: apply the vendor patch.

Do I need to reboot after patching?

For OS or kernel updates, yes. For most userland packages a systemctl restart <service> is enough. Any process that loaded the old shared library keeps using it until restarted, so when in doubt, reboot.

What is the CVSS score?

7.2 (high). Refer to the vendor advisory for the exact vector string.

Where is the official advisory?

See the References section at the bottom of this page; the vendor's URL is the authoritative source for affected builds and patched versions.

References

• Official vendor advisory: https://advisory.splunk.com/advisories/SVD-2026-0407
• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-20205

*Written by Sai Kiran Pandrala. Assembled from the official vendor advisory, NVD record, and CISA KEV listing on 2026-05-25. Always confirm against the vendor's advisory before applying changes in production.*