# CVE-2026-54638: td has pre-auth denial of service via unbounded memory allocation in proto.UnencryptedMessage.Decode

> Remote unauthenticated attackers can cause denial of service in the gotd/td library by triggering excessive memory allocation via crafted MTProto packets.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Jul 2026
- **Updated:** 29 Jul 2026
- **Also known as:** GHSA-whmm-qj9r-wvr2, GO-2026-6138

## What is CVE-2026-54638?

CVE-2026-54638 is a high-severity denial of service vulnerability in gotd td, published on 28 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

gotd/td is a T Telegram MTProto API client in Go. Prior to 0.145.1, proto.UnencryptedMessage.Decode in proto/unencrypted_message.go read attacker controlled dataLen from an unauthenticated MTProto unencrypted packet and allocated make([]byte, dataLen) before checking the remaining buffer, allowing remote unauthenticated denial of service through excessive memory allocation and CPU or garbage collection pressure. This issue is fixed in version 0.145.1.

Weakness: CWE-789 (Memory Allocation with Excessive Size Value), CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-54638?

3 open source packages ship an affected version, including github.com/gotd/td.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/gotd/td` | Go | All versions | 0.145.1 |
| `github.com/gotd/td` | Go | All versions | 0.145.1 |
| `github.com/gotd/td` | Go | All versions | 0.145.1 |

## How do I fix CVE-2026-54638?

Upgrade github.com/gotd/td to 0.145.1 or later.

## Is CVE-2026-54638 being exploited?

There is no known exploitation of CVE-2026-54638 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54638 and fix it if it is affected.

What it is: CVE-2026-54638 is a high-severity denial of service vulnerability in gotd td, published on 28 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-54638 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/gotd/td (Go): affected all versions; fixed in 0.145.1
- github.com/gotd/td (Go): affected all versions; fixed in 0.145.1
- github.com/gotd/td (Go): affected all versions; fixed in 0.145.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-54638/ (Markdown: https://insights.sbomify.com/CVE-2026-54638/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54638
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54638
- OSV: https://osv.dev/vulnerability/CVE-2026-54638

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54638/
Summaries are generated and may contain mistakes; the official description above is the record.