BusyBox TLS EUVD-2026-85425

Requires a BusyBox build compiled with its TLS support and operating in a TLS server role (the party that receives and processes a ClientKeyExchange handshake message) reachable over the network. Exploitation is pre-authentication and needs only a single crafted ClientKeyExchange message during the handshake - no user interaction, no credentials. The primary LIMITING factor is deployment: BusyBox's built-in TLS is minimal and most commonly used as a client (e.g. wget https), so instances acting as a network-facing TLS server are the exception, not the default, which sharply narrows the real exposed population despite BusyBox's ubiquity.

The provided CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, base 7.5) frames this as a remotely reachable, low-complexity, pre-authentication flaw whose only rated impact is availability (denial of service via heap corruption/crash), with no confidentiality or integrity impact claimed. That impact scoping is notable and slightly conservative: a pre-auth heap buffer overflow (CWE-131, incorrect buffer size calculation) frequently carries at least theoretical code-execution potential, so the C:N/I:N rating likely reflects that reliable code execution was not demonstrated rather than that it is impossible - treat A:H as the confirmed floor, not a ceiling. No EPSS score, no CISA KEV listing, and no POC are present in the supplied data, so exploitation status is 'no public exploit identified at time of analysis.' The realistic priority is moderate and highly conditional: while BusyBox itself is ubiquitous, the vulnerable path requires BusyBox to be acting as a TLS *server* that processes ClientKeyExchange messages - an uncommon deployment for BusyBox, whose TLS support is minimal and predominantly client-side (e.g. wget over HTTPS). Missing data: no EPSS, no KEV, no upstream BusyBox advisory or fix version in the references (only Red Hat tracking links), so remediation timeline and true affected-version range are unverified.

An attacker who can reach a network service backed by a BusyBox build acting as a TLS server sends a crafted TLS ClientKeyExchange message during the handshake. The unit-confusion error in the Montgomery reduction buffer allocation undersizes the buffer, and processing the crafted message overflows the heap, crashing the service (denial of service) with potential for further memory corruption. No public exploit code is identified at time of analysis, and exploitation is pre-authentication (PR:N) with low complexity (AC:L).