CVE-2026-39819: Invoking "go bug" follows symlinks in predictable temporary filenames in cmd/go

Severity: medium (CVSS 5.3 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-59

Description

The "go bug" command writes to two files with predictable names in the system temporary directory (for example, "/tmp"). An attacker with access to the temporary directory can create a symlink in one of these names, causing "go bug" to overwrite the target of the symlink.

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/763882
https://go.dev/issue/78584
https://groups.google.com/g/golang-announce/c/qcCIEXso47M
https://pkg.go.dev/vuln/GO-2026-4978

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