CVE-2026-108859 mcp-go through 1.2.1 Denial of Service via Unbounded POST Body Buffering
Remote attackers can exhaust server memory by sending oversized POST requests to the mcp-go library, causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-108859?
CVE-2026-108859 is a high-severity denial of service vulnerability in mark3labs mcp-go, published on 11 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
mcp-go through 1.2.1 contains a denial of service vulnerability in StreamableHTTPServer.ServeHTTP that allows remote unauthenticated attackers to exhaust memory by sending oversized POST bodies. Attackers can send arbitrarily large or many concurrent POST requests, read fully via io.ReadAll before validation, to degrade or OOM-kill the server process.
Weakness: CWE-770
Which versions are affected by CVE-2026-108859?
How do I fix CVE-2026-108859?
No fix has been published for CVE-2026-108859 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-108859 being exploited?
There is no known exploitation of CVE-2026-108859 in the wild and no public exploit code.
Sources
Also known as GHSA-c673-ppxx-9wvj.