# 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.

- **Severity:** High 7.6 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **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 available:** No
- **Published:** 27 Aug 2026
- **Updated:** 29 Aug 2026
- **Also known as:** GHSA-p943-9hp2-h27q

## 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 (Origin Validation Error)

## 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.

## Is CVE-2026-81099 being exploited?

There is no known exploitation of CVE-2026-81099 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81099 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-81099 in the wild and no public exploit code.

Affected product: timescale tiger-slack. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-81099/ (Markdown: https://insights.sbomify.com/CVE-2026-81099/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81099
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81099
- OSV: https://osv.dev/vulnerability/CVE-2026-81099

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81099/
Summaries are generated and may contain mistakes; the official description above is the record.