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VulnerabilityPublished Updated

CVE-2026-56855: Golang defaults · Previously, after a channel has been established, a malicious peer could send

Affects golang-defaultsSource GCVE Database

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Authoritative record:CVE-2026-56855· High 7.5

Not known to be exploited · CVSS 7.5 High.

Data as of 9 Nov 2026, 14:17 UTC

CVSS 3.1 base score
7.5High
How severe the flaw is on the 0–10 CVSS scale.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 2 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 9 Nov 2026.

What to do

Affected software

ProductAffectedFixed in
Ubuntu 26.10golang-1.26pkg:deb/ubuntu/golang-1.26?arch=source&distro=stonkingOther threatsAffected
  • 1.26.0-1 – 1.26.8-2
8 affected builds
Fixed in–
Ubuntu 26.10golang-1.27pkg:deb/ubuntu/golang-1.27?arch=source&distro=stonkingOther threatsAffected
  • 1.27.0-1 – 1.27~rc3-1
5 affected builds
Fixed in–
Ubuntu 26.10golang-defaultspkg:deb/ubuntu/golang-defaults?arch=source&distro=stonkingOther threatsAffected
  • =2:1.26~1
  • =2:1.27~1
Fixed in–
Ubuntu 26.04 LTSgolang-1.23pkg:deb/ubuntu/golang-1.23?arch=source&distro=resoluteOther threatsAffected
  • =1.23.10-1
Fixed in–
Ubuntu 26.04 LTSgolang-1.24pkg:deb/ubuntu/golang-1.24?arch=source&distro=resoluteOther threatsAffected
  • =1.24.4-1ubuntu1
  • =1.24.9-1
  • =1.24.13-2
Fixed in–
Ubuntu 26.04 LTSgolang-1.25pkg:deb/ubuntu/golang-1.25?arch=source&distro=resoluteOther threatsAffected
  • =1.25.0-0ubuntu1
  • =1.25.7-2
  • =1.25.14-1~ubuntu0.26.04.1
Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available that changes message handling to explicitly process RFC 4254 channel messages and treat unexpected messages as protocol errors, tearing down the connection instead of blocking. Users should update to fixed versions to remediate this issue.

Description

A vulnerability in golang-defaults allows a malicious peer to send crafted messages after a channel is established, causing the entire connection to deadlock. The issue arises from improper handling of RFC 4254 channel messages, where unexpected messages were buffered and blocked instead of being treated as protocol errors. The fix involves explicitly handling global requests and treating other unexpected messages as protocol errors, tearing down the connection to prevent deadlocks.

References

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