CVE-2026-39817: Invoking "go tool pack" does not sanitize output paths in cmd/go

Severity: medium (CVSS 5.9 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-07 · updated 2026-06-17
Weakness: CWE-787

Description

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.

Affected products

Go: before 1.25.10; from 1.26.0 before 1.26.3 — fixed in 1.25.10, 1.26.3

How to fix

Upgrade to a fixed version: Go 1.25.10, 1.26.3. Check the vendor advisory for mitigations.

References

https://go.dev/cl/767520
https://go.dev/issue/78778
https://groups.google.com/g/golang-announce/c/qcCIEXso47M
https://pkg.go.dev/vuln/GO-2026-4979

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