Vulnerability · Published Sep 29, 2026 · Assigned by GitHub_M

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

Medium 6.5

In plain English

A medium-severity uncontrolled resource consumption in russh from Eugeny. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 30% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)6.5Medium

Exploit odds (30 days)0.4%top 70.3% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:14	rust-russh	0.64.1-1	DEBIAN-CVE-2026-102821
Ubuntu:26.10	rust-russh	no fix listed	UBUNTU-CVE-2026-102821

Affected products (as reported)

Vendor	Product	Versions
Eugeny	russh	< 0.63.2

Weakness: CWE-400, CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/Eugeny/russh/security/advisories/GHSA-35g8-35p8-c8fw x_refsource_CONFIRM
https://github.com/Eugeny/russh/commit/a282af361ac99bc76b80876d1aae128e89dbf66b x_refsource_MISC
https://github.com/Eugeny/russh/releases/tag/v0.63.2 x_refsource_MISC