GO-2026-6355: golang.org/x/crypto (CVE-2026-56855)

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

CVSS 7.5 HighEPSS 0.0050 · 43rd percentile

Published by OSV at 2 Sept 2026, 19:12 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

Package	Ecosystem	Affected	Fixed in
golang.org/x/crypto	Go	<0.56.0	0.56.0

Identifiers

GO-2026-6355 · CVE-2026-56855

Weakness (CWE)

CWE-770

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

The golang.org/x/crypto module's ssh package is vulnerable in versions before 0.56.0. A malicious peer that has already established a channel can send crafted messages that deadlock the whole connection, causing a denial of service. Upgrade golang.org/x/crypto to version 0.56.0 or later.

Written 1 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
7.5	High	3.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	ADP (CISA-ADP)

CISA KEV Not listed.
EPSS 0.0050, the 43rd percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:13 UTC First seen by agentprime
31 Oct 2026, 14:13 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.