Medium [CVE-2026-56855] Denial of Service via crafted messages
This medium-severity Red Hat Linux advisory covers CVE-2026-56855 affecting Assisted Installer for Red Hat OpenShift Container Platform 2, Builds for Red Hat OpenShift, cert-manager Operator for Red Hat OpenShift.
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Summary
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. A flaw was found in golang.org/x/crypto/ssh.
This could lead to a deadlock of the entire connection, resulting in a Denial of Service (DoS) for the affected system. This vulnerability does not affect confidentiality or integrity.
Red Hat rates this issue as Moderate because the demonstrated availability impact is limited to the affected connection. Red Hat severity: Moderate — CVSS 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L).
Weakness: CWE-833.
Affected products named by the advisory: Assisted Installer for Red Hat OpenShift Container Platform 2; Builds for Red Hat OpenShift; cert-manager Operator for Red Hat OpenShift; Confidential Compute Attestation; and 34 more.
Affected products named by the advisory: Cryostat 4; External Secrets Operator for Red Hat OpenShift; Multicluster Engine for Kubernetes; OpenShift API for Data Protection; and 30 more.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
Mitigation checklist
- Red Hat is not aware of a practical mitigation that fully prevents this issue while maintaining affected SSH functionality. Where operationally possible, restrict SSH connectivity to trusted systems. Apply relevant Red Hat updates when they become available.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
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