What is CVE-2026-39834?

CVE-2026-39834 is a critical-severity vulnerability in Golang Crypto, classified under Integer Overflow or Wraparound. CVSS score: 9.1/10. Published 2026-05-22.

How severe is CVE-2026-39834?

Critical severity. CVSS v3 base score is 9.1 out of 10.

Integer overflow in Golang Crypto

CVE-2026-39834

When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the internal payload size calculation caused the write loop to spin indefinitely, sending empty packets without making progress. The size comparison now uses int64 to prevent truncation.

Vulnerability class: Integer Overflow

Published 2026-05-22 · last modified 2026-07-23.

CVSS v3 metric

CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H.

EPSS exploit prediction

EPSS: 0.006 (49.5th percentile), scored 2026-10-19.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 49th percentile — 49.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.006 · change: +0.001

Affected products

Golang Crypto
Golang.org/x/crypto Golang.org/x/crypto/ssh — versions 0

Weakness classification (CWE)

CWE-190 — Integer Overflow or Wraparound

References

go.dev/issue/79567 (Issue Tracking)
groups.google.com/g/golang-announce/c/a082jnz-LvI (Mailing List)
go.dev/cl/781663 (Issue Tracking)
pkg.go.dev/vuln/GO-2026-5020 (Vendor Advisory)

Frequently asked questions

What is CVE-2026-39834?: CVE-2026-39834 is a critical-severity vulnerability in Golang Crypto, classified under Integer Overflow or Wraparound. CVSS score: 9.1/10. Published 2026-05-22.
How severe is CVE-2026-39834?: Critical severity. CVSS v3 base score is 9.1 out of 10.