CVE-2019-20786

Vulnerability

Description

CVE-2019-20786 affects Pion DTLS, a Go implementation of DTLS 1.2. The vulnerability resides in handleIncomingPacket within conn.go [1]. The root cause is the absence of a check that enforces application data packets to have an epoch value other than 0 [1][4]. In the DTLS protocol, epoch 0 is reserved for the initial handshake phase; all post-handshake communication must use a non-zero epoch to ensure encryption and authentication.

Exploitation

A remote attacker who is able to send arbitrary network packets to a Pion DTLS endpoint can exploit this flaw after the DTLS handshake has successfully completed [1]. No prior authentication or session access is required; the attacker simply sends DTLS application data frames with epoch set to 0. The vulnerable library will process these frames as valid application data without decrypting or authenticating them [4].

Impact

Successful exploitation allows the attacker to inject arbitrary plaintext data that the receiving application treats as legitimate post-handshake traffic [1]. This bypasses the encryption and integrity guarantees of DTLS, effectively neutralizing the security of the established session. The injected data could trigger unintended application-level actions, leak information via responses, or corrupt shared state.

Mitigation

The issue was addressed in Pion DTLS release v1.5.2 by adding an explicit assertion that application data packets must have epoch not equal to 0 [2][4]. Users should upgrade to this version or later. No official workaround exists if upgrading is not possible, so applying the patch is strongly recommended.