CVE-2026-109375 Vercel CVE debrief

Who should care

Defenders and security teams responsible for Vercel deepsec deployments should assess exposure and apply patches or mitigations. Operators, platform administrators, and security teams should review compensating controls for exposed systems while remediation is scheduled and verified. They should also track exceptions, retest remediated assets, and close the item only after evidence is documented.

Why it matters

CVE-2026-109375 allows sandboxed code to write files outside the sandbox, potentially leading to unauthorized file writes and elevation of privileges. Defenders should assess exposure, apply patches, and monitor system integrity.

• Potential unauthorized file writes outside the sandbox
• Possible elevation of privileges for sandboxed code
• Required verification of patch application and system integrity

Technical summary

Vercel deepsec from 0.1.0 before 1.1.17 contains a link following vulnerability in extractTarballLocally that allows sandboxed code to write files outside the sandbox by planting links in result tarballs. Attackers controlling sandbox code can plant symbolic or hard links in the host data directory to write arbitrary files on the orchestrator host. The vulnerability can lead to unauthorized file writes and elevation of privileges. Defenders should assess exposure, apply patches, and monitor system integrity. The CVE record and source item provide details on the vulnerability.

Defensive priority

Medium

Recommended defensive actions

• Review and apply patches from vendor or community sources
• Restrict access to sensitive data and systems
• Monitor for suspicious activity and implement compensating controls
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The CVE record and source item provide details on the vulnerability in Vercel deepsec before 1.1.17, which allows sandboxed code to write files outside the sandbox by planting links in result tarballs. The vulnerability is a link following issue in extractTarballLocally. Attackers controlling sandbox code, such as a prompt-injected coding agent, can plant symbolic or hard links in the host data directory to write arbitrary files on the orchestrator host. Defenders should verify patch application and system integrity.

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.