Prevent DoS on deadlocked established channel in golang.org/x/crypto/ssh (CVE-2026-56855) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-56855

Prevent DoS on deadlocked established channel in golang.org/x/crypto/ssh

Answer in brief

CVE-2026-56855 records a Unknown severity vulnerability in Prevent DoS on deadlocked established channel in golang.org/x/crypto/ssh. The current sources do not mark it as known exploited. The current feed maps golang.org/x/crypto/golang.org/x/crypto/ssh (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 2, 2026Updated Sep 2, 2026Source checked Sep 2, 2026First seen by HOL Sep 2, 2026Material review Sep 2, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps golang.org/x/crypto/golang.org/x/crypto/ssh (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
golang.org/x/crypto/golang.org/x/crypto/sshgeneric	>=0 <0.56.0	0.56.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for golang.org/x/crypto/golang.org/x/crypto/ssh.
Review the reported fix. Update golang.org/x/crypto/golang.org/x/crypto/ssh to 0.56.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 2, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 2, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 2, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.