In js-libp2p's @libp2p/gossipsub module (versions >=15.0.0 <16.0.5), the default StrictSign policy in buildRawMessage.ts uses validateToRawMessage to verify message signatures. However, when the claimed author is an RSA peer ID lacking an inline public key, the verification process accepts a signature verified with an attacker-controlled key without binding that key to the claimed author. This allows an unauthenticated attacker to place a victim's RSA peer ID in the message's 'from' field, sign the message with the attacker's private key, and supply the attacker's public key as msg.key. Consequently, the message is accepted and propagated as if authored by the victim. Applications trusting message.from for critical functions like validation, authorization, or audit logging may process attacker-controlled data under false origin attribution. The issue is resolved in version 16.0.5.

An attacker can impersonate a victim peer ID by crafting messages that appear to originate from the victim, potentially causing applications relying on message origin for validation, authorization, accounting, moderation, reputation, or audit logging to process malicious data under false attribution. This can lead to unauthorized actions or incorrect trust decisions within affected applications. There is no indication of confidentiality or availability impact. No known exploits are reported in the wild.

Upgrade js-libp2p to version 16.0.5 or later, where this vulnerability is fixed. Until then, applications should be aware that messages from RSA peer IDs without inline public keys may be spoofed. No other vendor advisories or temporary mitigations are provided. Patch status is confirmed fixed in 16.0.5.