---
title: "CVE-2026-39834: golang.org/x/crypto vulnerable to infinite loop on large channel writes"
url: https://erroneo.us/security/cve/CVE-2026-39834/
description: "CVE-2026-39834 (golang.org/x/crypto (Go)): When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the internal…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-05-22
date_modified: 2026-07-07
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-39834"
kev: false
cvss: 9.1
epss: 0.00637
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-39834: golang.org/x/crypto vulnerable to infinite loop on large channel writes

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.6% , percentile 50: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 50% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes golang.org/x/crypto (Go) < 0.52.0, fixed in 0.52.0 . Check your lockfile, including transitive dependencies.

## What it is

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.

## Affected packages

- Go `golang.org/x/crypto` < 0.52.0 → fixed: 0.52.0

## Affected products (CVE record)

- golang.org/x/crypto golang.org/x/crypto/ssh: < 0.52.0

## Severity

- CISA-ADP CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H`
- GitHub CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 0.64% probability of exploitation activity in the next 30 days; percentile 50.

## Sources

- [GitHub Advisory GHSA-rm3j-f69w-wqmq](https://github.com/advisories/GHSA-rm3j-f69w-wqmq)
- [CVE.org record CVE-2026-39834](https://www.cve.org/CVERecord?id=CVE-2026-39834)
- [NVD entry CVE-2026-39834](https://nvd.nist.gov/vuln/detail/CVE-2026-39834)
- [go.dev](https://go.dev/issue/79567)
- [groups.google.com](https://groups.google.com/g/golang-announce/c/a082jnz-LvI)
- [go.dev](https://go.dev/cl/781663)
- [pkg.go.dev](https://pkg.go.dev/vuln/GO-2026-5020)

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Source page: https://erroneo.us/security/cve/CVE-2026-39834/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt