CVE-2026-39831 — Invoking bypass of FIDO/U2F security keys physical interaction in golang.org/x/crypto/ssh

Affected: golang.org/x/crypto/ssh

The Verify() method for FIDO/U2F security key types (sk-ecdsa-sha2-nistp256@openssh.com, sk-ssh-ed25519@openssh.com) did not check the User Presence flag. Signatures generated without physical touch were accepted, allowing unattended use of a hardware security key. To restore the previous behavior, return a "no-touch-required" extension in Permissions.Extensions from PublicKeyCallback.

USN-8447-1 — golang-go.crypto vulnerabilities

Affected: Ubuntu:Pro:16.04:LTS: golang-go.crypto, Ubuntu:Pro:18.04:LTS: golang-go.crypto, Ubuntu:Pro:20.04:LTS: golang-go.crypto, Ubuntu:Pro:22.04:LTS: golang-go.crypto, Ubuntu:Pro:24.04:LTS: golang-go.crypto, Ubuntu:Pro:26.04:LTS: golang-go.crypto

It was discovered that Go Cryptography did not properly handle SSH global request responses. A remote attacker could possibly use this issue to cause a denial of service. (CVE-2026-39830)

It was discovered that Go Cryptography did not properly verify user presence when using FIDO/U2F security keys. An attacker could possibly use this issue to bypass user presence verification for hardware security keys. This issue only affected Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 26.04 LTS. (CVE-2026-39831)

It was discovered that Go Cryptography did not properly serialize SSH agent key constraint extensions. An attacker could possibly use this issue to bypass intended key usage restrictions. This issue only affected Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 26.04 LTS. (CVE-2026-39832)

It was discovered that Go Cryptography did not properly enforce the confirm-before-use constraint in the SSH agent keyring. An attacker could possibly use this issue to use SSH keys without the required user confirmation. (CVE-2026-39833)

It was discovered that Go Cryptography had an integer overflow when handling large SSH channel writes. A remote attacker could possibly use this issue to cause a denial of service. (CVE-2026-39834)

It was discovered that Go Cryptography did not properly check certificate authority key revocation. An attacker could possibly use this issue to bypass certificate authority revocation checks. This issue only affected Ubuntu 1…

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CVE-2026-39831 — Invoking bypass of FIDO/U2F security keys physical interaction in golang.org/x/crypto/ssh

USN-8447-1 — golang-go.crypto vulnerabilities