# CVE-2026-116774: russh SSH library zero maximum packet size denial of service

Source: https://junglewise.ai/threats/cve-2026-116774-russh-is-a-rust-ssh-client-and-server-library-that-includes-an  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-27. Updated: 2026-10-27  
License: CC BY 4.0 with a link back

CVE-2026-116774 · Severity: medium · CVSS 4.3 · Published 2026-10-27

russh is a Rust SSH client and server library used in applications that need SSH functionality. An attacker can exploit a flaw in how the library handles SSH channel setup by declaring a zero-sized maximum packet, causing the affected application's write operations to hang indefinitely. This allows an authenticated attacker against a server, or any attacker against a client connecting to a malicious server, to cause a denial of service by stranding channels and connections without an error notification.

Technologies: [russh (crates.io)](https://junglewise.ai/threats/technologies/crates-io-russh). Vendors: [crates.io](https://junglewise.ai/threats/vendors/crates-io).

## Quick answers

**Is CVE-2026-116774 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-116774 being exploited in the wild.

**How severe is CVE-2026-116774?** Medium severity, with a CVSS score of 4.3, published 27 October 2026.

**Which products and versions are affected?** russh (crates.io) >= 0.60.0, <= 0.64.1, ECOSYSTEM:introduced=0.60.0,fixed=0.65; Russh 0.60.0 to 0.64.x.

**Is there a fix for CVE-2026-116774?** Yes. russh (crates.io): upgrade to 0.65 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-116774 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-116774?** Check whether you run russh (crates.io) or Russh 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 0.65 or later

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


## Technical details

The vulnerability exists in channel-open packet parsing (versions 0.60.0 to 0.64.x) where a peer-declared maximum_packet_size of zero is accepted and passed to ChannelTx::poll_writable. The asynchronous write paths (Channel::data, Channel::make_writer, Channel::into_stream) calculate a writable size of zero and remain pending forever because window adjustments cannot satisfy a static zero packet maximum. The fix in 0.65.0 rejects zero-valued maximum_packet_size parameters at the protocol parsing stage.

## Affected products

- russh russh 0.60.0 to 0.64.x

## Identifiers

- CVE-2026-116774
- GHSA-fw5c-8223-6h42

## Timeline

- 2026-10-27: disclosed
- 2026-10-25: patched: Version 0.65.0 released

## References

- [https://github.com/Eugeny/russh/commit/39cb9dbaa37caf555d34c6c22efa3bbbff9e186c](https://github.com/Eugeny/russh/commit/39cb9dbaa37caf555d34c6c22efa3bbbff9e186c)
- [https://github.com/Eugeny/russh/releases/tag/v0.65.0](https://github.com/Eugeny/russh/releases/tag/v0.65.0)

## 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 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)
- [russh SSH agent unbounded memory allocation via constraint records](https://junglewise.ai/threats/cve-2026-111061-russh-is-a-rust-ssh-client-and-server-library-that-includes-an)