CVE-2026-102823 · GHSA-47hw-gvq5-r2gm

russh: Client-side channel-scoped Handler callbacks fire for channel IDs the client never opened

Risk score: 53/100
CVSS: 7.5 v3.1
Exploit chance (30 days): 0.3%
Published: 29 Sep 2026

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What to know

What it is: Russh is a Rust SSH client and server library. Prior to 0.63.1, client_read_authenticated in russh/src/client/encrypted.rs forwards CHANNEL_DATA, CHANNEL_EXTENDED_DATA, CHANNEL_EOF, CHANNEL_CLOSE, CHANNEL_OPEN_FAILURE, CHANNEL_SUCCESS, CHANNEL_FAILURE, and CHANNEL_REQUEST subtypes exit-status, exit-signal, and xon-xof…
Affected: russh (rust) <= 0.63.0
Fix: Upgrade russh to 0.63.1 or later.
Exploitation: No known exploitation

Story map

Story map: the flaws, the fix, how it unfolded and what it connects to. Boxes link to the record or article.

At a glance

russh: Yellow, plan it in. Russh is a Rust SSH client and server library. Prior to 0.63.1, client_read_authenticated in russh/src/client/encrypted.rs forwards CHANNEL_DATA, CHANNEL_EXTENDED_DATA, CHANNEL_EOF, CHANNEL_CLOSE, CHANNEL_OPEN_FAILURE, CHANNEL_SUCCESS, CHANNEL_FAILURE, and CHANNEL_REQUEST subtypes exit-status, exit-signal, and xon-xof…

The flaws

CVE-2026-102823: Client-side channel-scoped Handler callbacks fire for channel IDs the client never opened (CVSS 7.5 · EPSS 0%)
CVE-2026-102821: Russh: Unbounded memory exhaustion via CHANNEL_OPEN flood during a client-stalled rekey (CVSS 6.5 · EPSS 0%)

The fix

Upgrade russh: 0.63.1 · 0.63.2 or later on your release line

Who is exposed: russh (rust) <= 0.63.0

Where it stands

Public proof of concept

Connects to

Same weakness: Denial of service (CWE-400). 253 other warnings in 30 days

Why it is Yellow

CVSS 7.5 high
Remotely exploitable without logging in

Affected packages

Package	Ecosystem	Vulnerable	Fixed in
russh	rust	<= 0.63.0	0.63.1

References

Original description

Russh is a Rust SSH client and server library. Prior to 0.63.1, client_read_authenticated in russh/src/client/encrypted.rs forwards CHANNEL_DATA, CHANNEL_EXTENDED_DATA, CHANNEL_EOF, CHANNEL_CLOSE, CHANNEL_OPEN_FAILURE, CHANNEL_SUCCESS, CHANNEL_FAILURE, and CHANNEL_REQUEST subtypes exit-status, exit-signal, and xon-xoff to public client::Handler callbacks without confirming that the ChannelId belongs to a channel the client opened and established. A malicious SSH server can send lifecycle events for predicted, unopened, unconfirmed, or released channel identifiers, causing application panics or corrupting command completion and exit-code tracking. This issue is fixed in version 0.63.1.

Last activity 29 Sep 2026. Patch Forecast updates every hour.