CVE-2026-81099 Timescale tiger-slack DNS Rebinding via Disabled Host Header Allow-List
Attackers can bypass host header checks to access the local Slack MCP server via DNS rebinding, requiring explicit configuration of the host allow-list.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-81099?
CVE-2026-81099 is a high-severity server-side request forgery vulnerability in timescale tiger-slack, published on 27 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
tiger-slack started its MCP HTTP transport without enabling the host allow-list the underlying SDK provides. mcp/src/httpServer.ts called the shared httpServerFactory helper and never set the DNS-rebinding-protection option, so the transport accepted a request whatever host it named, and a page in a browser could point a name it controlled at the address the server was bound to and drive the locally reachable Slack MCP server through the visitor's browser. The fix passes the option explicitly alongside a dependency update; the update alone would not have closed it. The repository publishes no release that brackets the fix, so the affected boundary is the commit preceding it.
Weakness: CWE-346
Which versions are affected by CVE-2026-81099?
How do I fix CVE-2026-81099?
No fix has been published for CVE-2026-81099 yet. Limit exposure of the affected software until one is available.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-81099 being exploited?
There is no known exploitation of CVE-2026-81099 in the wild and no public exploit code.
Sources
Also known as GHSA-p943-9hp2-h27q.