CVE-2026-111057: Mercury: Unauthenticated Remote Code Execution in /api/terminals - access control bypass

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.4%, percentile 37: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 37% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes mercury (PyPI) >= 3.0.0, <= 3.2.3, fixed in 3.2.4. Check your lockfile, including transitive dependencies.

What it is

Mercury is a Python framework for sharing Jupyter notebooks as web applications and dashboards. From 3.0.0 until 3.2.4, a missing comma in BLOCKEDPATTERNS concatenates the /lab and /api/terminals regular-expression literals. Requests to /api/terminals therefore bypass the anonymous endpoint blocklist and reach Jupyter Server's terminal API. An unauthenticated attacker can use the resulting interactive operating-system shell to execute commands and access data available to the Mercury process. This issue is fixed in version 3.2.4.

From the GitHub advisory

Summary A missing comma in mercuryapp/blockhandler.py's BLOCKEDPATTERNS list causes the blocklist to fail to cover the /api/terminals endpoint. As a result, any unauthenticated attacker can spawn a full, interactive OS-level shell on the host running Mercury.

Details The blocklist in mercuryapp/blockhandler.py is defined as:

The missing comma between the first and the second line causes Python to merge the rules, therefore the actual list that is blocked looks like this:

/lab...(?:/.)?/api/terminals(?:/.)? (the first two lines joined together) /api/shutdown(?:/.)? /files(?:/.)?

A direct request to /api/terminals does not match any of the 3 blocklist rules and is therefore not blocked, reaching Jupyter Server's built-in terminal API, which spawns a real OS shell accessible over a WebSocket connection. No authentication, account, session or pre-existing access to Mercury is required.

Weakness type: CWE-185, CWE-284.

Product: mercury (PyPI) · Assigned by: GitHub_M · Published: 2026-10-19

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• FIRST EPSS (model of 2026-10-21): 0.44% probability of exploitation activity in the next 30 days; percentile 37.

Timeline

• 2026-10-19 — CVE record last updated
• 2026-10-19 — CVE record published by GitHub_M
• 2026-10-19 — GitHub-reviewed advisory GHSA-f8c7-rwf9-fmgm published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-f8c7-rwf9-fmgm github.com
2. CVE.org record CVE-2026-111057 cve.org
3. NVD entry CVE-2026-111057 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical PyPI advisories · Today’s Security Digest