CVE-2026-42505: Handshakes which used Encrypted Client Hello could be de-anonymized by a passive network observer due to a dis

Routine

MEDIUM 5.3REMOTEUPGRADE

CVE-2026-42505 is a medium-severity flaw (CVSS 5.3) affecting go. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 68%)
CISA exploited list	No
Weakness	CWE-201
Published	2026-07-08
Last modified	2026-10-25

Publisher (CNA): Go Project · Vendor: golang

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-08 17:17 UTCPublished CVE record published
2026-10-25 17:10 UTCUpdated Record last modified

golang go UPGRADE

Affected: >= 1.23.0 and < 1.25.12 · >= 1.26.0 and < 1.26.5 · 1.27 rc1

Fixed in: 1.25.12, 1.26.5

Safe to downgrade to: a release before 1.23.0

1. Check installed version

apt-cache policy go || rpm -q go || go --version

2. UPGRADE to 1.25.12 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade go

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade go

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 1.23.0 (Debian / Ubuntu)

apt-cache madison go sudo apt install go=<VERSION_BEFORE_1.23.0> sudo apt-mark hold go

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list go sudo dnf downgrade go-<VERSION_BEFORE_1.23.0> sudo dnf versionlock add go

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Advisories and coverage

Official advisories

Amazon Linux 2023 ALAS: ALAS2023-2026-3153 (medium): soci-snapshotter 2026-10-12
Amazon Linux 2023 ALAS: ALAS2023-2026-3180 (medium): amazon-ecr-credential-helper 2026-10-12
Amazon Linux 2023 ALAS: ALAS2023-2026-3205 (medium): docker 2026-10-12
Amazon Linux 2023 ALAS: ALAS2023-2026-3206 (medium): oci-add-hooks 2026-10-12
Amazon Linux 2 ALAS: ALAS2DOCKER-2026-143 (medium): soci-snapshotter 2026-10-12
Amazon Linux 2 ALAS: ALAS2DOCKER-2026-145 (medium): amazon-ecr-credential-helper 2026-10-12

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-42505?

go: upgrade to 1.25.12, 1.26.5. Exact commands for each OS are on this page.

Is CVE-2026-42505 being exploited?

CVE-2026-42505 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-42505 affect?

CVE-2026-42505 affects go. Severity is medium (CVSS 5.3). 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.

How urgent is CVE-2026-42505?

Priority 32/100. Remotely exploitable, no login, no user action

Software pages

Go (Golang) vulnerabilities

Related CVEs

CVE-2026-39822 HIGH 7.8 UPGRADE On Unix systems, opening a file in an os.Root improperly follows symlinks to locations outside of the Root whe

References

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