# CVE-2026-90813: cosmicstack-labs mercury-agent shell command validation bypass

Source: https://junglewise.ai/threats/cve-2026-90813-cosmicstack-labs-mercury-agent-shell-command-validation-bypass  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-14. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-90813 · Severity: medium · CVSS 4.3 · Published 2026-09-14

Mercury-agent is an AI agent framework that executes shell commands on behalf of users. A flaw in the shell command validation logic allows attackers to bypass file access restrictions by using environment variable expansion (e.g., $HOME) to read files outside the intended workspace boundary without triggering approval prompts. This could allow disclosure of sensitive local files.

Technologies: [Cosmicstack Labs Mercury Agent](https://junglewise.ai/threats/technologies/mercury-agent). Vendors: [Cosmicstack Labs](https://junglewise.ai/threats/vendors/cosmicstack-labs).

## Quick answers

**Is CVE-2026-90813 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-90813 being exploited in the wild.

**How severe is CVE-2026-90813?** Medium severity, with a CVSS score of 4.3, published 14 September 2026.

**Which products and versions are affected?** Cosmicstack Labs Mercury Agent up to 1.1.13.

**Is there a fix for CVE-2026-90813?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-90813 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-90813?** Check whether you run Cosmicstack Labs Mercury Agent at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a time-of-check–time-of-use (TOCTOU) flaw in the shell command permission gate. The `checkShellCommand()` function in src/capabilities/permissions.ts validates commands in their pre-expansion form, checking for literal absolute paths (/, ~/, ..), before shell expansion occurs. However, the safe-read pattern whitelist includes patterns like `head *` which match commands with unexpanded variables. When the validated string is later executed via `spawn(..., { shell: true })` in src/capabilities/shell/run-command.ts, shell variable expansion occurs, allowing $HOME and other environment variables to resolve to absolute paths outside the workspace. An attacker can craft commands like `head $HOME/secret.txt` that pass validation as safe-read but execute with expanded privileges, bypassing the cwdOnly boundary check that would normally require user approval for absolute-path file access. No authentication bypass or privilege elevation is required; the attack relies on Mercury invoking run_command with attacker-controlled input.

## Affected products

- cosmicstack-labs mercury-agent up to 1.1.13

## Timeline

- 2026-09-14: disclosed
- exploited: Public exploit available; issue report filed but project has not yet responded

## References

- [https://github.com/cosmicstack-labs/mercury-agent/](https://github.com/cosmicstack-labs/mercury-agent/)
- [https://github.com/cosmicstack-labs/mercury-agent/issues/95](https://github.com/cosmicstack-labs/mercury-agent/issues/95)

## Related threats

- [cosmicstack-labs mercury-agent server-side request forgery in GitHub API handler](https://junglewise.ai/threats/cve-2026-90814-cosmicstack-labs-mercury-agent-server-side-request-forgery-in)
- [cosmicstack-labs mercury-agent privilege escalation in shell permission check](https://junglewise.ai/threats/cve-2026-90812-cosmicstack-labs-mercury-agent-privilege-escalation-in-shell)
- [Cosmicstack Labs Mercury Agent shell permission bypass via wc](https://junglewise.ai/threats/cve-2026-90811-cosmicstack-labs-mercury-agent-shell-permission-bypass-via-wc)
- [CosmicStack mercury-agent authorization bypass in shell command validation](https://junglewise.ai/threats/cve-2026-90810-cosmicstack-mercury-agent-authorization-bypass-in-shell-command)