Russh: Unbounded memory exhaustion via CHANNEL_OPEN flood during a client-stalled rekey (CVE-2026-102821) | HOL Guard CVE

Medium · CVSS 6.5CVE-2026-102821

Russh: Unbounded memory exhaustion via CHANNEL_OPEN flood during a client-stalled rekey

Answer in brief

CVE-2026-102821 records a Medium severity (CVSS 6.5) vulnerability in Russh: Unbounded memory exhaustion via CHANNEL_OPEN flood during a client-stalled rekey. The current sources do not mark it as known exploited. The current feed maps Eugeny/russh (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 29, 2026Updated Sep 29, 2026Source checked Sep 29, 2026First seen by HOL Sep 29, 2026Material review Sep 29, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 6.5
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 6.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Eugeny/russh (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Eugeny/russhgeneric	<0.63.2	0.63.2

Recommended response

Check inventory. Check lockfiles and deployed manifests for Eugeny/russh.
Review the reported fix. Update Eugeny/russh to 0.63.2 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 29, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 29, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 29, 2026

Sources and claim methodology

Upstream source description

Russh is a Rust SSH client and server library. Prior to 0.63.2, an authenticated remote peer can send SSH_MSG_KEXINIT without the required SSH_MSG_KEX_ECDH_INIT and then flood SSH_MSG_CHANNEL_OPEN messages while SessionKexState::InProgress prevents priority_receiver in russh/src/server/session.rs from being drained. The server continues processing network input and enqueues a ChannelOpenReply for each request on an unbounded channel, allowing one connection to grow memory until the process is terminated. This issue is fixed in version 0.63.2.

Quoted source text, attributed separately from HOL analysis.