High severity · published Sep 2, 2026
CVE-2026-56855
Prevent DoS on deadlocked established channel in golang.org/x/crypto/ssh
7.5
CVSS
0.5%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 43% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
GO
golang.org/x/crypto/ssh · golang.org/x/crypto
before 0.56.0 · source: vendor
CR
Crypto · Golang
before 0.56.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-56855
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-56855
Patch
https://go.dev/cl/826524
Issue Tracking
https://go.dev/issue/81317
Mailing List
https://groups.google.com/g/golang-announce/c/1y3fb2np35U
Vendor Advisory
https://pkg.go.dev/vuln/GO-2026-6355
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