What is CVE-2026-39817?

CVE-2026-39817 is a medium-severity vulnerability in Golang Go, classified under Out-of-bounds Write. CVSS score: 5.9/10. Published 2026-05-07.

How severe is CVE-2026-39817?

Medium severity. CVSS v3 base score is 5.9 out of 10.

Buffer overflow in Golang Go

CVE-2026-39817

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.

Vulnerability class: Buffer Overflow

Published 2026-05-07 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.002 (4.7th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 5th percentile — 4.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: -0.000

Affected products

Golang Go
Go Toolchain Cmd/go — versions 0, 1.26.0-0

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

References

go.dev/issue/78778 (Issue Tracking)
go.dev/cl/767520 (Patch)
groups.google.com/g/golang-announce/c/qcCIEXso47M (Mailing List, Issue Tracking)
pkg.go.dev/vuln/GO-2026-4979 (Vendor Advisory)

Frequently asked questions

What is CVE-2026-39817?: CVE-2026-39817 is a medium-severity vulnerability in Golang Go, classified under Out-of-bounds Write. CVSS score: 5.9/10. Published 2026-05-07.
How severe is CVE-2026-39817?: Medium severity. CVSS v3 base score is 5.9 out of 10.