5.3Medium
Golang Go
CVE-2026-42505
Handshakes which used Encrypted Client Hello could be de-anonymized by a passive network observer due to a disclosure of pre-shared key identities in the unencrypted client hello.
What this means for your business
- It affects Golang Go. It matters if your company, or a supplier that handles your data, runs it.
- An attacker can use it remotely, over a network, without a login, and without anyone at your company clicking anything.
- FIRST's prediction model gives it a 0.4% chance of attack attempts being seen in the next 30 days, ranking above 32% of all known flaws.
What to do
- 1Check whether your company or your suppliers run Golang Go, and which version. The affected versions are listed further down this page.
- 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.
Not sure if your company is exposed?
Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.
Scoring
- CVSS
- 5.3 (v3.1)
- Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N- Weakness
- CWE-201
- Assigned by
- security@golang.org
Dates
- Published
- 2026-07-08
- Last modified
- 2026-09-16
- Sources
- NVD
Affected products
- Golang Go1.23.0 - 1.25.12, 1.26.0 - 1.26.5, 1.27
As listed in the NVD configuration data. Not a statement about your estate.