CVE-2026-104480 in libdave
Summary
by MITRE • 10/02/2026
Discord libdave before 1.2.0 did not reject an MLS Welcome message when the resulting group roster contained an unrecognized participant. An attacker in control of the DAVE signaling path (the voice gateway, or an equivalent position able to add, alter, or withhold signaling messages to a client) could cause affected clients to accept an unauthorized member into the end-to-end encrypted media session, compromising the confidentiality and integrity of audio and video.
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Analysis
by VulDB Data Team • 10/02/2026
The vulnerability identified in Discord's libdave library prior to version 1.2.0 represents a critical failure in cryptographic protocol enforcement within the Media over DTLS (MLS) implementation used for end-to-end encrypted voice and video communications. The core technical flaw lies in the handling of MLS Welcome messages, which are responsible for adding new participants to an existing group session. Specifically, the library failed to validate whether all members listed in a newly formed or updated roster were recognized by the client's local state. This oversight allowed a malicious actor who controls the DAVE signaling path—such as the voice gateway server or any intermediary capable of injecting, altering, or withholding signaling messages—to manipulate the group membership list without detection. By inserting an unrecognized participant into the Welcome message, the attacker could force affected clients to accept this unauthorized entity into the encrypted media session.
From a technical perspective, this flaw violates fundamental principles of secure multi-party communication protocols where identity verification is paramount. In standard MLS implementations, every client must maintain a consistent view of the group state and verify that all participants are legitimate members authorized by the current group context. The absence of rigorous validation for unrecognized identifiers in the roster means that the cryptographic handshake proceeds even when the integrity of the participant set cannot be guaranteed. This creates a scenario where confidentiality is compromised because sensitive audio or video data may be transmitted to an entity that should not have access, and integrity is undermined as the attacker can potentially intercept or manipulate streams under the guise of being a valid member.
The operational impact of this vulnerability is severe for users relying on Discord's private voice channels, direct messages with media sharing, or any feature utilizing end-to-end encryption. An adversary in position to control signaling traffic could exploit this flaw to eavesdrop on conversations that are presumed to be secure. Since the attack requires controlling the DAVE signaling path, it typically targets scenarios where network infrastructure is compromised or when an attacker has achieved a privileged position within the communication pipeline, such as through man-in-the-middle attacks at the ISP level or compromise of intermediate servers. The ability to inject unauthorized members effectively breaks the trust model of the application, allowing for potential surveillance and data exfiltration without triggering standard security alerts associated with connection anomalies.
This vulnerability aligns closely with CWE-295 Improper Certificate Validation and CWE-347 Improper Verification of Cryptographic Signature, as it involves a failure to properly verify the authenticity and integrity of cryptographic material before accepting new state changes. In terms of MITRE ATT&CK framework behaviors, this exploitation technique relates to T1078 Valid Accounts or more specifically techniques involving manipulation of authentication processes within specific applications (T1529). It also reflects aspects of protocol-level attacks where an adversary abuses the handshake mechanism to establish unauthorized access, similar to concepts found in session hijacking but applied at the cryptographic group membership level.
To mitigate this risk, organizations and users must ensure that Discord clients are updated to version 1.2.0 or later, which includes patches for libdave to enforce strict validation of participant identities within MLS Welcome messages. Network administrators should also implement monitoring for anomalous signaling traffic patterns that might indicate attempts to manipulate group membership lists. Furthermore, relying on end-to-end encryption requires confidence in the underlying implementation; therefore, keeping software up to date is essential to maintain the confidentiality and integrity guarantees promised by these security features. Regular audits of third-party libraries used in communication stacks are recommended to identify similar logic flaws before they can be exploited in production environments.