# CVE-2026-42189: Russh SSH library denial of service in keyboard-interactive auth

Source: https://junglewise.ai/threats/cve-2026-42189-russh-ssh-library-denial-of-service-in-keyboard-interactive-auth  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-08. Updated: 2026-05-13  
License: CC BY 4.0 with a link back

CVE-2026-42189 · Severity: high · CVSS 7.5 · Published 2026-05-08

A denial-of-service vulnerability exists in russh, a library used to implement SSH servers in Rust. An unauthenticated attacker can crash the server by sending a single specially crafted packet during the login process, specifically when multi-factor authentication (like 2FA or TOTP) is enabled. This results in a complete service outage for all users and can be repeated to prevent the server from restarting.

Technologies: [russh (crates.io)](https://junglewise.ai/threats/technologies/crates-io-russh), [Eugeny Tabby](https://junglewise.ai/threats/technologies/tabby). Vendors: [crates.io](https://junglewise.ai/threats/vendors/crates-io), [Eugeny](https://junglewise.ai/threats/vendors/eugeny).

## Quick answers

**Is CVE-2026-42189 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42189 being exploited in the wild.

**How severe is CVE-2026-42189?** High severity, with a CVSS score of 7.5, published 8 May 2026.

**Which products and versions are affected?** Binarty Warpgate <= 0.23.0; russh (crates.io) SEMVER:introduced=0,fixed=0.60.1; Eugeny Tabby < 0.60.1.

**Is there a fix for CVE-2026-42189?** Yes. russh (crates.io): upgrade to 0.60.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-42189 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-42189?** Check whether you run Binarty Warpgate, russh (crates.io) or Eugeny Tabby at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- russh (crates.io): upgrade to 0.60.1 or later

  ```sh
  cargo update -p russh
  ```


## Technical details

A memory allocation vulnerability (CWE-770/CWE-789) exists in `russh/src/server/encrypted.rs` within the `read_userauth_info_response` function. The handler decodes a `u32` integer from a client's `SSH_MSG_USERAUTH_INFO_RESPONSE` packet and uses it directly in `Vec::with_capacity()` without validating it against the actual remaining packet size. An unauthenticated attacker can provide a large value (e.g., 0x10000000), forcing the server to attempt a multi-gigabyte allocation that triggers an Out-of-Memory (OOM) crash. This occurs during the keyboard-interactive authentication flow before any credentials are validated. The issue is fixed in version 0.60.1 by capping the allocation capacity based on the remaining packet data.

## Affected products

- Eugeny russh < 0.60.1

## Identifiers

- CVE-2026-42189
- GHSA-f5v4-2wr6-hqmg

## Timeline

- 2026-04-20: disclosed
- 2026-04-24: advisory
- 2026-04-24: patched: Fixed in version 0.60.1

## References

- [https://api.github.com/users/coreyleavitt](https://api.github.com/users/coreyleavitt)
- [https://github.com/coreyleavitt](https://github.com/coreyleavitt)
- [https://api.github.com/users/coreyleavitt/gists%7B/gist_id%7D](https://api.github.com/users/coreyleavitt/gists%7B/gist_id%7D)
- [https://api.github.com/users/coreyleavitt/repos](https://api.github.com/users/coreyleavitt/repos)
- [https://avatars.githubusercontent.com/u/18317330?v=4](https://avatars.githubusercontent.com/u/18317330?v=4)
- [https://api.github.com/users/coreyleavitt/events%7B/privacy%7D](https://api.github.com/users/coreyleavitt/events%7B/privacy%7D)

## Related threats

- [russh SSH server signature algorithm mismatch in publickey auth](https://junglewise.ai/threats/cve-2026-111062-a-russh-ssh-server-accepts-a-publickey-authentication-whose)
- [russh SSH agent confirmation bypass](https://junglewise.ai/threats/cve-2026-116794-russh-is-a-rust-ssh-client-and-server-library-that-includes-an)
- [russh SSH library zero maximum packet size denial of service](https://junglewise.ai/threats/cve-2026-116774-russh-is-a-rust-ssh-client-and-server-library-that-includes-an)
- [russh memory exhaustion via unbounded EXT_INFO packets](https://junglewise.ai/threats/cve-2026-116773-russh-is-a-rust-ssh-client-and-server-library-that-includes-an)
- [russh's SSH agent server is susceptible to unbound allocations via repeated SSH_AGENT_CONSTRAIN_CONFIRM messages](https://junglewise.ai/threats/cve-2026-116696-russh-is-a-rust-ssh-client-and-server-library-that-includes-an)