CVE-2026-42505 Invoking Encrypted Client Hello privacy leak in crypto/tls
A passive network observer can de-anonymize TLS handshakes using Encrypted Client Hello by reading pre-shared key identities in the unencrypted client hello.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42505?
CVE-2026-42505 is a medium-severity vulnerability in Golang Go, published on 8 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-201
Which versions are affected by CVE-2026-42505?
2 open source packages ship an affected version, including golang and stdlib. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
golang Bitnami | All versions | 1.25.12, 1.26.5, 1.27.0 |
stdlib Go | All versions | 1.25.12, 1.26.5, 1.27.0-rc.2 |
Linux distribution packages (3)
go-passbolt-cli openSUSE:Tumbleweed | All versions | 0.5.2-1.1 |
mihomo openSUSE:Tumbleweed | All versions | 1.19.28-1.1 |
tekton-cli openSUSE:Tumbleweed | All versions | 0.46.0-1.1 |
Products include Golang Go.
How do I fix CVE-2026-42505?
Upgrade golang to a fixed version for your release line: 1.25.12, 1.26.5 or 1.27.0.
Is CVE-2026-42505 being exploited?
There is no known exploitation of CVE-2026-42505 in the wild and no public exploit code.
Other vulnerabilities in Golang Go
- CVE-2020-0601 Microsoft Windows CryptoAPI Spoofing
- CVE-2026-27143 Missing bound checks can lead to memory corruption in safe Go in cmd/compile
- CVE-2024-24790 Unexpected behavior from Is methods for IPv4-mapped IPv6 addresses in net/netip
- CVE-2023-39320 Arbitrary code execution via go.mod toolchain directive in cmd/go
- CVE-2023-24540 Improper handling of JavaScript whitespace in html/template
Sources
Also known as AZL-92306, AZL-92312, BELL-CVE-2026-42505, BIT-golang-2026-42505, CLEANSTART-2026-AZ00076, CLEANSTART-2026-DS58516 and 1800 more.