Meshtastic Firmware CVE-2025-53627

Exploitation requires the attacker to possess a valid shared channel key for a channel the victim participates in; with that key the adversary crafts a direct message that omits the pki_encrypted flag, causing firmware (version 2.5 through before 2.7.15) to silently fall back to legacy AES-256-CTR decryption while end-user apps (Web, iOS, Android, SDK-based) display it as if PKI-encrypted. The principal limiting factor is knowledge of the shared channel key - though for the default/public channel this key is well-known, lowering the barrier - and the impact is confined to spoofing/impersonation and loss of end-to-end-encryption assurance, with no confidentiality or availability consequence. Affected deployments are those running vulnerable firmware prior to 2.7.15 together with client apps lacking PKI-versus-legacy indication.

This is a moderate-severity integrity flaw, not a high-urgency priority. The provided CVSS of 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N) reflects a network-reachable, low-complexity attack with no privileges or user interaction, but impact is limited to partial integrity (I:L) with no confidentiality or availability loss - consistent with a message-spoofing/downgrade weakness rather than code execution. A public exploit exists (GitHub Security Advisory GHSA-377p-prwp-4hwf is flagged as an exploit reference), so publicly available exploit code exists; however this is NOT active exploitation - the CVE is not in CISA KEV, so treat POC availability and exploitation as distinct signals. No EPSS score and no SSVC decision data were provided, so automatability and widespread-exploitation probability cannot be quantified from this input. A key caveat: although the CVSS vector encodes PR:N (unauthenticated), the description makes clear that exploitation requires the adversary to already know a shared channel key - this is a real material precondition that the CVSS base metrics understate, so the practical attacker barrier is higher than PR:N alone suggests.

An attacker who already possesses a Meshtastic channel's shared symmetric key (e.g., the well-known default channel key or a leaked group key) crafts a direct message that omits the pki_encrypted flag. The firmware silently decrypts it with legacy AES-256-CTR and the victim's app renders it indistinguishably from a genuine PKI end-to-end-encrypted DM, letting the attacker impersonate another user. A public proof of concept is referenced in the GitHub advisory.