# CVE-2026-56855 — golang.org/x/crypto golang.org/x/crypto/ssh

> As of 2026-09-03, CVE-2026-56855 is a HIGH-severity vulnerability in golang.org/x/crypto golang.org/x/crypto/ssh, CVSS v3.1 7.5, EPSS 0.1% (6.6th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-56855 as of 2026-09-03; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-09-03

## What is CVE-2026-56855?

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.

The record classifies CVE-2026-56855 under weakness class [CWE-770](https://intel.threadlinqs.com/cwe/CWE-770). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 33 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 7.5 — HIGH (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **EPSS (FIRST):** 0.1% probability of exploitation in the next 30 days, higher than 6.6% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-09-02, last modified 2026-09-03

## Is CVE-2026-56855 being exploited?

It currently carries a trending score of 31 in the Threadlinqs vulnerability feed.

## Affected products and versions

- **golang.org/x/crypto**: golang.org/x/crypto/ssh

## How to fix CVE-2026-56855

No vendor patch reference has been recorded for CVE-2026-56855 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-56855

No threat campaign in the Threadlinqs corpus currently references CVE-2026-56855, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, FIRST EPSS. Last verified by Threadlinqs on 2026-09-04. This product uses the NVD API but is not endorsed or certified by the NVD.

**Other references**

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

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-56855
Full detection coverage and IOCs for threats exploiting CVE-2026-56855 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp