CVE-2026-54638

td has pre-auth denial of service via unbounded memory allocation in proto.UnencryptedMessage.Decode

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.

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.

The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.

CVE-2026-54638 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.145.1); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Fixed in v0.145.1 by validating dataLen against the remaining buffer length before allocation (commit 9d5d1f31e).

1. What is CVE-2026-54638? CVE-2026-54638 is a high-severity allocation of resources without limits or throttling vulnerability in github.com/gotd/td (go), affecting versions < 0.145.1. It is fixed in 0.145.1. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
2. How severe is CVE-2026-54638? CVE-2026-54638 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/gotd/td are affected by CVE-2026-54638? github.com/gotd/td (go) versions < 0.145.1 is affected.
4. Is there a fix for CVE-2026-54638? Yes. CVE-2026-54638 is fixed in 0.145.1. Upgrade to this version or later.
5. Is CVE-2026-54638 exploitable, and should I be worried? Whether CVE-2026-54638 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-54638 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-54638? Upgrade github.com/gotd/td to 0.145.1 or later.