7.5

CVE-2026-56855: Prevent DoS on deadlocked established channel in golang.org/x/crypto/ssh

Analyzed
AliasesUBUNTU-CVE-2026-56855DEBIAN-CVE-2026-56855CGA-2226-6mcp-7v8w
Published 02-09-2026Last modified 03-09-2026

Vulnerability summary

CVE-2026-56855 is a high (CVSS 7.5) vulnerability in golang crypto. EPSS estimates a 0.50% chance of exploitation in the next 30 days, higher than 42.9% of scored vulnerabilities.

Priority
Prioritisesevere

Severe, CVSS 7.5 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 1% (FIRST, 03-11-2026)

Source freshness unavailable

How is this decided?
CVSS score
7.5/10
010
High · v3.1 (CVE.org)
EPSS score
0.50%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 52 · Related 53
OPENSUSE-SU-2026:11727-1OPENSUSE-SU-2026:11731-1OPENSUSE-SU-2026:11732-1OPENSUSE-SU-2026:11752-1OPENSUSE-SU-2026:11871-1OPENSUSE-SU-2026:11920-1

Timeline

  1. 02-09-2026
    PublishedVulnerability first disclosed.
  2. 03-09-2026
    Last modifiedVulnerability information updated.

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 metrics

6 scores · 6 sources · 1 version

EPSS trend

Probability

0.50%

Chance of exploitation in the next 30 days

Percentile

43%

Versus all other CVEs

30-day change

No change 0.00 pp

From 0.50% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Chainguard200 products
  • aactl< 0.4.12-r75
  • acm-controllerAll versions (No fix recorded)
  • acm-controller-fipsAll versions (No fix recorded)
  • act< 0.2.89-r10
  • actions-runner-controllerAll versions (No fix recorded)

1 vendor · 200 products · Showing 200 of 4054

References

11 links
Show all 11 references