Vulnerability · Published Sep 2, 2026 · Assigned by Go
CVE-2026-56855Prevent DoS on deadlocked established channel in golang.org/x/crypto/ssh
High 7.5
In plain English
A high-severity resource allocation without limits in golang.org/x/crypto/ssh from golang.org/x/crypto. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 43% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Previously, after a channel has been established, a malicious peer could send crafted messages that would deadlock the entire connection. Now, we handle all RFC 4254 channel messages; global requests are handled explicitly. Then, treat all other messages as a protocol error and tear the connection down instead of buffering and blocking.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:9 | buildah | 2:1.43.4-2.el9_8 | ALSA-2026:90424 |
| AlmaLinux:9 | buildah | 2:1.43.3-2.el9_8 | ALSA-2026:70640 |
| AlmaLinux:9 | buildah-tests | 2:1.43.3-2.el9_8 | ALSA-2026:70640 |
| AlmaLinux:9 | buildah-tests | 2:1.43.4-2.el9_8 | ALSA-2026:90424 |
| Debian:12 | golang-go.crypto | no fix listed | DEBIAN-CVE-2026-56855 |
| Debian:13 | golang-go.crypto | no fix listed | DEBIAN-CVE-2026-56855 |
| Debian:14 | golang-go.crypto | 1:0.56.0-1 | DEBIAN-CVE-2026-56855 |
| Go | golang.org/x/crypto | 0.56.0 | GO-2026-6355 |
| Rocky Linux:9 | buildah | 2:1.43.3-2.el9_8 | RLSA-2026:70640 |
| Rocky Linux:9 | buildah | 2:1.43.4-2.el9_8 | RLSA-2026:90424 |
| Ubuntu:22.04:LTS | golang-1.17 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:22.04:LTS | golang-1.20 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:22.04:LTS | golang-1.21 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:24.04:LTS | golang-1.21 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:22.04:LTS | golang-1.23 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:24.04:LTS | golang-1.23 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:26.04:LTS | golang-1.23 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:22.04:LTS | golang-1.24 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:24.04:LTS | golang-1.24 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:26.04:LTS | golang-1.24 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:22.04:LTS | golang-1.25 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:24.04:LTS | golang-1.25 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:26.04:LTS | golang-1.25 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:22.04:LTS | golang-1.26 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:24.04:LTS | golang-1.26 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:26.04:LTS | golang-1.26 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:26.10 | golang-1.26 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:26.10 | golang-1.27 | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:22.04:LTS | golang-defaults | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:24.04:LTS | golang-defaults | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:26.04:LTS | golang-defaults | no fix listed | UBUNTU-CVE-2026-56855 |
| Ubuntu:26.10 | golang-defaults | no fix listed | UBUNTU-CVE-2026-56855 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| golang.org/x/crypto | golang.org/x/crypto/ssh | 0 – before 0.56.0 |
Weakness: CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H