UBUNTU-CVE-2026-116127: Medium severity ubuntu/starlet vulnerability
Starlet versions before 0.33 for Perl send a body in responses to HEAD requests, corrupting the next response on a persistent or pipelined connection. The request method is not passed to the response writer, so whatever body the application returns for a HEAD request is sent. With Plack::Middleware::Head the body is empty, but an HTTP/1.1 response without a Content-Length header still gets the chunked encoding terminator. Responses with status 204 or 304 are also sent with their body. Pipelined GET and HEAD requests keep the connection open even when keep-alive is disabled, which is the default. A client or proxy reading the connection takes the extra bytes as the start of the next response, which may desynchronize a proxy that shares the connection across clients.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Starletto a version that resolves this vulnerability.Fixed in 0.33
Event History
Frequently Asked Questions
Who is most exposed to this issue?
Deployments using a proxy that reuses a backend connection across different clients are most exposed, because response desynchronization on that shared connection can affect subsequent clients.
Does disabling keep-alive prevent exploitation?
No. Pipelined GET and HEAD requests keep the connection open even when keep-alive is disabled, and disabled keep-alive is the default.
Does Plack::Middleware::Head fully mitigate the issue?
No. Although Plack::Middleware::Head makes the response body empty, an HTTP/1.1 response without Content-Length can still send the chunked-encoding terminator, leaving extra bytes that can desynchronize the next response.