CVE-2026-42501: A malicious module proxy can exploit a flaw in the go command's validation of module checksums to bypass check

Routine

HIGH 7.5UPGRADE

CVE-2026-42501 is a high-severity flaw (CVSS 7.5) affecting go. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A malicious module proxy can exploit a flaw in the go command's validation of module checksums to bypass checksum database validation. This vulnerability affects any user using an untrusted module proxy (GOMODPROXY) or checksum database (GOSUMDB). A malicious module proxy can serve altered versions of the Go toolchain. When selecting a different version of the Go toolchain than the currently installed toolchain (due to the GOTOOLCHAIN environment

Why this priority

High severity

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 86%)
CISA exploited list	No
Weakness	CWE-347
Published	2026-05-07
Last modified	2026-06-17

Publisher (CNA): Go Project · Vendor: golang

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-07 20:16 UTCPublished CVE record published
2026-06-17 10:47 UTCUpdated Record last modified

golang go UPGRADE

Affected: < 1.25.10 · >= 1.26.0 and < 1.26.3

Fixed in: 1.25.10, 1.26.3

Safe to downgrade to: a release before 1.26.0

1. Check installed version

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

2. UPGRADE to 1.25.10 (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 1.26.0 (Debian / Ubuntu)

apt-cache madison go sudo apt install go=<VERSION_BEFORE_1.26.0> 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_1.26.0> 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.

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-2026-42501?

go: upgrade to 1.25.10, 1.26.3. Exact commands for each OS are on this page.

Is CVE-2026-42501 being exploited?

CVE-2026-42501 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-2026-42501 affect?

CVE-2026-42501 affects go. Severity is high (CVSS 7.5). A malicious module proxy can exploit a flaw in the go command's validation of module checksums to bypass checksum database validation. This vulnerability affects any user using an untrusted module proxy (GOMODPROXY) or checksum database (GO

How urgent is CVE-2026-42501?

Priority 30/100. High severity

Software pages

Go (Golang) vulnerabilities

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References

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