Medium

Sensitive data exfiltration via style attribute validation flaw in Splunk classic dashboards

IdentifiersCVE-2026-20257CWE-20· Improper Input Validation

CVE-2026-20257 is an improper input validation vulnerability in Splunk classic dashboards affecting Splunk Enterprise versions below 10.2.4, 10.0.7, 9.4.12, and 9.3.13, and Splunk Cloud Platform versions below 10.3.2512.13, 10.2.2510.15, 10.1.2507.23, and 9.3.2411.132. Classic dashboard panels do not fully validate CSS style attribute values, which allows a low-privileged Splunk user without the admin or power roles to craft a malicious dashboard that causes browser requests to external domains outside the configured Trusted Domains List when viewed by a higher-privileged user. The issue is described as a CSS input validation flaw and enables client-side data exfiltration from the victim user's browser.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation allows a low-privileged user to exfiltrate sensitive data from the browser context of a higher-privileged Splunk user, such as an administrator, to attacker-controlled external domains. The impact is limited to scenarios where the victim is induced to view or initiate the crafted dashboard content, but can expose sensitive browser-accessible data and session-related information handled by Splunk Web.

Mitigation

If you can’t patch tonight, do this now.

No complete workaround is provided in the advisory content. Until patched, reduce exposure by restricting which users can create or modify classic dashboards, monitoring for suspicious or newly created dashboards, enforcing strict trusted-domain controls, minimizing Splunk Web exposure where feasible, and reducing opportunities for phishing or social engineering that could cause privileged users to open untrusted dashboards.

Remediation

Patch, then assume compromise.

Upgrade Splunk Enterprise to 10.2.4, 10.0.7, 9.4.12, or 9.3.13 or later. Upgrade Splunk Cloud Platform to 10.3.2512.13, 10.2.2510.15, 10.1.2507.23, or 9.3.2411.132 or later. Apply the vendor fixes across all supported deployments using classic dashboards.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

SplunkSplunkapplication

SplunkSplunk Cloud Platformapplication

SplunkSplunk Enterpriseapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

1 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

1 SOURCESView more in app

cyber security newsNews

Jun 11, 2026

Multiple Splunk Enterprise Vulnerabilities Allow Attackers to Execute Malicious Script

A medium-severity improper input validation vulnerability in Splunk Enterprise classic dashboards involving CSS input validation that can enable data exfiltration to external domains.

What this page doesn’t show

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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-20257

NVD

nvd.nist.gov/vuln/detail/CVE-2026-20257

MITRE CWE · CWE-20

Improper Input Validation

Vendor Advisory

advisory.splunk.com/advisories/SVD-2026-0607