MCP Toolbox for Databases: Permissive Cross-domain Security Policy with Untrusted Domains
CVE-2026-9739 is a critical-severity permissive cross-domain security policy with untrusted domains vulnerability in MCP Toolbox for Databases from Google, with a CVSS 4.0 base score of 9.4 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. The record lists version PR 3054 (Fix CORS bypass) as the first without the flaw, so updating MCP Toolbox for Databases to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.28% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update MCP Toolbox for Databases to PR 3054 (Fix CORS bypass) or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| MCP Toolbox for Databases | before PR 3054 (Fix CORS bypass) | PR 3054 (Fix CORS bypass) |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Attack requirements
- NoneThe attack does not depend on a particular deployment or configuration.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- ActiveA user must deliberately do something unusual, such as dismissing a warning.
- Confidentiality (vulnerable system)
- HighSerious loss of confidentiality on the vulnerable system.
- Integrity (vulnerable system)
- HighSerious loss of integrity on the vulnerable system.
- Availability (vulnerable system)
- HighSerious loss of availability on the vulnerable system.
- Confidentiality (other systems)
- HighSerious loss of confidentiality on systems beyond the vulnerable one.
- Integrity (other systems)
- HighSerious loss of integrity on systems beyond the vulnerable one.
- Availability (other systems)
- HighSerious loss of availability on systems beyond the vulnerable one.
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. Scored by CNA (google.com).
Official description
Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790). During the beta phase, we implemented `allowed-origins` and `allowed-hosts` flags to align with MCP security guidelines. However, the hardcoded `Access-Control-Allow-Origin: *` header in the SSE initialization handler was inadvertently retained. This vulnerability specifically impacts users connecting via Toolbox using SSE under specification v2024-11-05.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Permissive Cross-domain Security Policy with Untrusted Domains
The product uses a web-client protection mechanism such as a Content Security Policy (CSP) or cross-domain policy file, but the policy includes untrusted domains with which the web client is allowed to communicate.
How developers prevent this class of flaw
- Define a restrictive Content Security Policy or cross-domain policy file.
- Avoid using wildcards in the CSP / cross-domain policy file. Any domain matching the wildcard expression will be implicitly trusted, and can perform two-way interaction with the target server.
- For Flash, modify crossdomain.xml to use meta-policy options such as 'master-only' or 'none' to reduce the possibility of an attacker planting extraneous cross-domain policy files on a server.
More Permissive Cross-domain Security Policy with Untrusted Domains vulnerabilities (CWE-942)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other references
Other vulnerabilities in MCP Toolbox for Databases
- 8.6 High severity
- 7.5 High severity
- 7.5 High severity
- 7.7 High severity
- 9.8 Critical severity
- 7.5 High severity
Recent Permissive Cross-domain Security Policy with Untrusted Domains vulnerabilities
- 8.1 High severity
- 8.1 High severity
- 9.6 Critical severity
- 8.8 High severity
- 8.1 High severity
- 9.6 Critical severity
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