CVE-2026-54638

Unbounded memory allocation in proto.UnencryptedMessage.Decode in github.com/gotd/td

### Impact A remote, unauthenticated attacker can cause excessive memory allocation (and resulting CPU / GC pressure, potentially OOM termination) by sending a crafted unencrypted MTProto packet. `(*proto.UnencryptedMessage).Decode` read an attacker-controlled 32-bit `dataLen` field and immediately allocated a buffer of that size via `make([]byte, dataLen)` **before** validating that the underlying buffer actually contained that many bytes. A 20-byte packet declaring a ~1.75 GB payload (e.g. `dataLen = 0x70000000`) forces the runtime to provision and zero-initialize a multi-gigabyte heap allocation before the length is rejected. Unencrypted messages are part of the unauthenticated MTProto handshake path, so no credentials or established session are required to reach the vulnerable code. Impact is limited to availability; there is no evidence of memory corruption, out-of-bounds access, or code execution. ### Patches Fixed in **v0.145.1** by validating `dataLen` against the remaining buffer length before allocation (commit `9d5d1f31e`). ### Workarounds Upgrade to v0.145.1 or later. There is no in-process workaround for affected versions short of avoiding exposure of the unauthenticated MTProto parsing path to untrusted peers.

gotd/td es un cliente API MTProto de Telegram T en Go. Antes de la versión 0.145.1, proto.UnencryptedMessage.Decode en proto/unencrypted_message.go leía un dataLen controlado por el atacante de un paquete MTProto no cifrado no autenticado y asignaba make([]byte, dataLen) antes de verificar el búfer restante, lo que permitía una denegación de servicio remota no autenticada a través de una asignación excesiva de memoria y presión de CPU o de recolección de basura. Este problema se solucionó en la versión 0.145.1.