CVE-2026-56855: Golang defaults · Previously, after a channel has been established, a malicious peer could send
Affects golang-defaultsSource GCVE Database
Not known to be exploited · CVSS 7.5 High.
Data as of 9 Nov 2026, 14:17 UTC
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 2 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.10golang-1.26pkg:deb/ubuntu/golang-1.26?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.10golang-1.27pkg:deb/ubuntu/golang-1.27?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.10golang-defaultspkg:deb/ubuntu/golang-defaults?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSgolang-1.23pkg:deb/ubuntu/golang-1.23?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSgolang-1.24pkg:deb/ubuntu/golang-1.24?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSgolang-1.25pkg:deb/ubuntu/golang-1.25?arch=source&distro=resoluteOther threats | Affected
| 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
- ubuntu.com/security/CVE-2026-56855 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-56855 (opens in a new tab)
- go.dev/cl/826524 (opens in a new tab)
- go.dev/issue/81317 (opens in a new tab)
- groups.google.com/g/golang-announce/c/1y3fb2np35U (opens in a new tab)
- pkg.go.dev/vuln/GO-2026-6355 (opens in a new tab)