CVE-2026-55240 msgbyte CVE debrief

Who should care

Tianji administrators and users, as well as security teams responsible for monitoring and protecting against potential exploitation of this vulnerability. Affected operator, platform, vulnerability-management, and security-team impact should be carefully evaluated to ensure proper mitigation and remediation.

Why it matters

CVE-2026-55240 is a critical remote code execution vulnerability in Tianji that requires immediate attention from administrators and security teams. The vulnerability allows an unauthenticated user to execute server-side JavaScript, potentially leading to command execution, secret disclosure, data modification, or service disruption. Affected versions should be upgraded to version 1.31.29 or later to mitigate the vulnerability.

• Potential command execution on the Tianji server
• Possible secret disclosure or data modification
• Service disruption due to exploitation

Technical summary

Tianji is vulnerable to remote code execution via the lodash template evaluate pattern in survey feed templates. An unauthenticated user can submit a response to a survey, which can lead to command execution, secret disclosure, data modification, or service disruption. The vulnerability is caused by the formatString() function in src/server/utils/template.ts passing survey feedTemplate and monitor notification templates to lodash template(), while the default evaluate pattern remains enabled. A workspace administrator can store an evaluate block using the <% code %> form, and the public survey.submit endpoint renders a survey template when an unauthenticated user submits a response.

Defensive priority

Tianji administrators and users should prioritize upgrading to version 1.31.29 or later to address the remote code execution vulnerability.

Recommended defensive actions

• Upgrade Tianji to version 1.31.29 or later
• Review and restrict usage of survey feed templates and monitor notification templates
• Implement additional security measures to detect and prevent exploitation
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record and source item provide details on the Tianji vulnerability, including the affected version and fixed version. The vulnerability is confirmed to exist in versions prior to 1.31.29. Defenders should verify the existence of affected product deployments in managed environments and review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.