CVE-2026-39817: The "go tool pack" subcommand (usually used only by the compiler as an internal tool with known-good inputs) d

Routine

MEDIUM 5.9UPGRADE

CVE-2026-39817 is a medium-severity flaw (CVSS 5.9) affecting go. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The "go tool pack" subcommand (usually used only by the compiler as an internal tool with known-good inputs) does not sanitize output filenames. Extracting a malicious archive file with the "pack" subcommand can write files to arbitrary locations on the filesystem.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	Required
EPSS exploit chance	0.2% (top 94%)
CISA exploited list	No
Weakness	CWE-787
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 10:42 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-2026-39817?

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

Is CVE-2026-39817 being exploited?

CVE-2026-39817 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-2026-39817 affect?

CVE-2026-39817 affects go. Severity is medium (CVSS 5.9). The "go tool pack" subcommand (usually used only by the compiler as an internal tool with known-good inputs) does not sanitize output filenames. Extracting a malicious archive file with the "pack" subcommand can write files to arbitrary loc

How urgent is CVE-2026-39817?

Priority 22/100. No elevated risk signals yet.

Software pages

Go (Golang) vulnerabilities

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References

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