---
id: "CVE-2026-116773"
kind: "vulnerability"
aliases: ["CVE-2026-116773"]
title: "russh: malicious SSH server can exhaust client memory before authentication"
severity: "medium"
cvss: 4.3
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["package", "russh", "rust", "ssh-client"]
not_affected_if: ["server-only-use", "trusted-hosts-only"]
published_at: "2026-10-27T21:18:05+00:00"
first_seen_at: "2026-10-27T21:29:21+00:00"
updated_at: "2026-10-27T21:30:22+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-116773", "first_seen_at": "2026-10-27T21:29:21+00:00"}]
---

# russh: malicious SSH server can exhaust client memory before authentication

The russh Rust SSH library's client accepts repeated packets using a private message number 7 before authentication and stores every extension name without a limit. A malicious SSH server can make a connecting client grow in memory for the lifetime of the session until it runs out.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the russh version in `Cargo.lock` with `grep -A1 'name = "russh"' Cargo.lock`
- Look for any version below `0.65.0` in your dependency tree with `cargo tree -i russh`

## Fix

- Upgrade the russh crate to `0.65.0` or later with `cargo update -p russh`

## Timeline

- 2026-10-27T21:29:21+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-116773

## From the sources

russh is a Rust SSH client and server library that includes an SSH agent protocol implementation. Prior to 0.65.0, the client Session::process_packet path in russh/src/client/encrypted.rs accepts repeated packets encoded with russh's private msg::EXT_INFO = 7 before authentication, while the standards-compliant EXT_INFO message number 82 does not reach the affected handler. The handle_ext_info function appends every parsed extension name to received_extensions without clearing, deduplicating, or bounding the vector. A malicious SSH server that deliberately sends private message number 7 can therefore retain an unbounded number of attacker-controlled extension names for the session lifetime, causing progressive client memory exhaustion. This issue is fixed in version 0.65.0.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_