Security Digest · Vulnerability record
CVE-2026-9739: MCP Toolbox for Databases vulnerable to DNS rebinding attacks
Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790).
CVSS 9.4 Critical EPSS 0.2% · p14
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 and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.2%, percentile 14: FIRST’s model estimates a 0.2% chance of exploitation activity in the next 30 days, higher than 14% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Only applies if your dependency tree includes
github.com/googleapis/mcp-toolbox(Go) < 1.2.0, fixed in 1.2.0. Check your lockfile, including transitive dependencies.
What it is
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.
From the GitHub advisory
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.
Weakness type: CWE-942.
Product: github.com/googleapis/mcp-toolbox (Go) · Assigned by: Google · Published: 2026-05-27
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| Go | github.com/googleapis/mcp-toolbox | < 1.2.0 | 1.2.0 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| MCP Toolbox for Databases | < PR 3054 (Fix CORS bypass) |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| 4.0 | 9.4 Critical | 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 | |
| GitHub | 4.0 | 9.4 | 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 |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Attack requirements: none
- Privileges required: none (no login)
- User interaction: active
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).
- CISA SSVC assessment: exploitation none, automatable no, technical impact total.
- FIRST EPSS (model of 2026-10-21): 0.24% probability of exploitation activity in the next 30 days; percentile 14.
Timeline
- — CVE record published by Google
- — CVE record last updated
- — GitHub-reviewed advisory GHSA-7pf3-8xx7-rvhf published (critical)
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-7pf3-8xx7-rvhf github.com
- CVE.org record CVE-2026-9739 cve.org
- NVD entry CVE-2026-9739 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- github.com github.com
- github.com github.com