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CVE-2026-102821— Russh: Unbounded memory exhaustion via CHANNEL_OPEN flood during a client-stalled rekey

Quick assessment

Affected
Eugeny russh
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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_re

CVSS 6.5 · Medium
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I. Basic Information for CVE-2026-102821

Vulnerability Information

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Vulnerability Title
Russh: Unbounded memory exhaustion via CHANNEL_OPEN flood during a client-stalled rekey
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Eugeny russh < 0.63.2 -

II. Public POCs for CVE-2026-102821

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III. Intelligence Information for CVE-2026-102821

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Other References for CVE-2026-102821 (3)

Same Patch Batch · Eugeny · 2026-09-29 · 6 CVEs total

CVE-2026-102823 7.5 HIGH russh: Client-side channel-scoped Handler callbacks fire for channel IDs the client never
CVE-2026-102820 6.2 MEDIUM pageant: Out-of-bounds read / oversized allocation in `pageant` MemoryMap::read via a mali
CVE-2026-102824 4.3 MEDIUM Russh: Missing X25519 zero-point validation in hybrid ML-KEM key exchange
CVE-2026-102822 3.7 LOW russh: negotiating a MAC-requiring block cipher (CTR/CBC) with mac=none causes a slice-ind
CVE-2026-102825 3.7 LOW Russh: Configured server auth-attempt cap is not enforced in the USERAUTH_REQUEST runtime

IV. Related Vulnerabilities

Same product: russh
Same vendor: Eugeny
Same weakness: CWE-400

V. Comments for CVE-2026-102821

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