Fiber is Vulnerable to Denial of Service via Flash Cookie Unbounded Allocation

QFinch assessment

The use of the fiberflash cookie can force an unbounded allocation on any server. A crafted 10-character cookie value triggers an attempt to allocate up to 85GB of memory via unvalidated msgpack deserialization. No authentication is required. Every GoFiber v3 endpoint is affected regardless of whether the application uses flash messages.

Potential impact

Unauthenticated remote Denial of Service (CWE-789). Anyone running a gofiber v3.0.0 or v3 server is affected. The flash cookie parsing is hardcoded.

Technical context

Regardless of configuration, the flash cookie is checked: The cookie value is hex-decoded and passed directly to msgpack deserialization with no size or content validation: https://github.com/gofiber/fiber/blob/f8f34f642fb3682c341ede7816e7cf861aa7df89/redirect.goL371 The auto-generated tinylib/msgp deserialization reads a uint32 array header from the attacker-controlled byte stream and passes it directly to make() with no bounds check: https://github.com/gofiber/fiber/blob/f8f34f642fb3682c341ede7816e7cf861aa7df89/redirectmsgp.goL242 where zb0002, bts, err = msgp.ReadArrayHeaderBytes(bts) translates the attacker-controlled value into the element count and make(redirectionMsgs, zb0002) performs the unbounded allocation So we can craft a gofiber cookie that will force a huge allocation: curl -H "Cookie: fiberflash=dd7fffffff" http://localhost:5000/hello The cookie val is a hex-encoded msgpack array32 header: - dd = msgpack array32 marker - 7fffffff = 2 147 483 647 elements