What’s Vulnerable › Vulnerabilities

CVE-2026-56855: Prevent DoS on deadlocked established channel in golang.org/x/crypto/ssh

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-02 · updated 2026-09-04
• Weakness: CWE-770

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 products

• golang.org/x/crypto/ssh: before 0.56.0 — fixed in 0.56.0
• Golang.Org/X/Crypto: before 0.56.0 — fixed in 0.56.0

How to fix

Upgrade to a fixed version: golang.org/x/crypto/ssh 0.56.0; Golang.Org/X/Crypto 0.56.0. Check the vendor advisory for mitigations.

References

• https://go.dev/cl/826524
• https://go.dev/issue/81317
• https://groups.google.com/g/golang-announce/c/1y3fb2np35U
• https://pkg.go.dev/vuln/GO-2026-6355

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