Orgs Urged to Patch Mercury 3.2.4 to Stop Terminal Shell Access via Missing Comma CVE-2026-111057
A missing comma in Mercury versions 3.0.0 through 3.2.3 allows attackers to access terminal shells. Version 3.2.4 resolves the critical vulnerability.
Key points
- CVE-2026-111057 allows unauthenticated remote code execution via Jupyter Server's terminal API.
- The flaw affects Mercury versions 3.0.0 up to and including 3.2.3.
- Version 3.2.4 contains the necessary patch to restore endpoint blocking.
Mercury versions 3.0.0 through 3.2.3 contain a critical vulnerability that allows unauthenticated remote code execution. The flaw stems from a syntax error in the application's blocklist configuration. Attackers can bypass security controls to access interactive operating system shells. Version 3.2.4 fixes this issue. Teams managing Mercury deployments must verify their current version immediately.
How it unfolded
- The vulnerability exists in the `block_handler.py` file within the Mercury Python framework.
- A missing comma caused two regular expression patterns to concatenate incorrectly.
- This syntax error allowed requests to `/api/terminals` to bypass the anonymous endpoint blocklist.
- The National Vulnerability Database assigned CVE-2026-111057 with a CVSS score of 10.
Who is affected
Organisations using the mljar Mercury package for sharing Jupyter notebooks as web applications are at risk. Versions 3.0.0 and newer, up to 3.2.3 inclusive, are vulnerable. The flaw allows any external attacker to spawn a full OS-level shell on the host. No authentication or prior access is required. The process running Mercury determines the level of access an attacker gains.
Our take on the response
The vendor has released version 3.2.4 to address this critical issue. The fix restores the intended separation of blocked patterns. This prevents the terminal API from being exposed to anonymous users. The rapid release of a patch suggests high priority for the maintainers. Users should apply the update to mitigate the risk of remote code execution.
Who needs to act first
Teams usually prioritise systems exposed to the internet or untrusted networks. Check whether any Mercury instances are publicly accessible before rolling out updates. Test the patched version in a non-production environment to ensure compatibility. Back up current configurations and data before applying changes. If immediate patching is not possible, restrict network access to the affected ports. Monitor logs for suspicious terminal connection attempts from unknown sources.
What to do and how to stay safe: Mercury
- Identify all servers and containers running Mercury versions 3.0.0 through 3.2.3.
- Upgrade to version 3.2.4 or later once the vendor provides the update.
- Restrict network access to Mercury endpoints to trusted IP addresses only.
- Monitor system logs for unexpected terminal sessions or command executions.
Step-by-step guide: Vulnerability Prioritization: How to Rank Risks Without Wasting Time
General security guidance from the Patch Observer newsroom. It is not confirmed advice from the organisations named in this story.
Frequently asked questions
What is the CVSS score for CVE-2026-111057?
The National Vulnerability Database rates the vulnerability as critical with a CVSS score of 10.
Which versions of Mercury are affected by this flaw?
Versions 3.0.0 through 3.2.3 are affected. Version 3.2.4 contains the fix.
Is authentication required to exploit this vulnerability?
No, the flaw allows unauthenticated attackers to execute commands on the host system.
