# CVE-2026-42189: Russh: Pre-auth DoS via unbounded allocation in keyboard-interactive auth

> A malicious client can crash russh-based SSH servers via unbounded allocation in keyboard-interactive authentication without credentials.

- **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:** 8 May 2026
- **Updated:** 11 May 2026
- **Also known as:** DEBIAN-CVE-2026-42189, GHSA-f5v4-2wr6-hqmg, UBUNTU-CVE-2026-42189

## What is CVE-2026-42189?

CVE-2026-42189 is a high-severity denial of service vulnerability in Eugeny russh, published on 8 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Russh is a Rust SSH client & server library. Prior to version 0.60.1, a pre-authentication denial-of-service vulnerability exists in the server's keyboard-interactive authentication handler. A malicious client can crash any russh-based server that implements keyboard-interactive auth (e.g., for 2FA/TOTP) with a single malformed packet, requiring no credentials. This issue has been patched in version 0.60.1.

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

## Which versions are affected by CVE-2026-42189?

2 open source packages ship an affected version, including russh. It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `russh` | crates.io | All versions | 0.60.1 |
| `russh` | crates.io | All versions | 0.60.1 |

Products: Russh Project Russh, Warpgate Project Warpgate.

## How do I fix CVE-2026-42189?

Upgrade russh to 0.60.1 or later.

## Is CVE-2026-42189 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42189 exists.

## Other vulnerabilities in Eugeny russh

- [CVE-2024-43410](https://insights.sbomify.com/CVE-2024-43410/): Russh has an OOM Denial of Service due to allocation of untrusted amount (high 7.5)
- [CVE-2025-54804](https://insights.sbomify.com/CVE-2025-54804/): Russh is missing an overflow check during channel windows adjust (medium 6.5)
- [CVE-2023-28113](https://insights.sbomify.com/CVE-2023-28113/): russh may use insecure Diffie-Hellman keys (medium 5.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42189 and fix it if it is affected.

What it is: CVE-2026-42189 is a high-severity denial of service vulnerability in Eugeny russh, published on 8 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42189 exists.

Affected packages and fixed versions:
- russh (crates.io): affected all versions; fixed in 0.60.1
- russh (crates.io): affected all versions; fixed in 0.60.1

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-2026-42189/ (Markdown: https://insights.sbomify.com/CVE-2026-42189/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42189
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42189
- OSV: https://osv.dev/vulnerability/CVE-2026-42189

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42189/
Summaries are generated and may contain mistakes; the official description above is the record.