9.1

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-39833

CVE-2026-39833: Invoking key constraints not enforced in golang.org/x/crypto/ssh/agent

The in-memory keyring returned by NewKeyring() silently accepted keys with the ConfirmBeforeUse constraint but never enforced it. The key would sign without any confirmation prompt, with no indication to the caller that the constraint was not in effect. NewKeyring() now returns an error when unsupported constraints are requested.

(GitHub Advisory)

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CVE-2026-39833

CVE-2026-39833:

9.1

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

SSVC / BOD 26-04 ↗

Exploitation NoneAutomatable YesTech Impact Total

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Package Name	Ecosystem	Vulnerable Versions	First Patched Version
golang.org/x/crypto/ssh/agent	go	< 0.52.0	0.52.0

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability, CVE-2026-39833, is a logic flaw in the golang.org/x/crypto/ssh/agent package where key constraints, specifically the ConfirmBeforeUse constraint, were not enforced. The analysis of the provided patches reveals that the Add methods in both the server-side keyring (ssh/agent/server.go) and the client-side client (ssh/agent/client.go) were responsible for this vulnerability. These functions would accept keys with constraints but would not process or enforce them, leading to a situation where a key that should require user confirmation for signing operations could be used without any such confirmation. The patch addresses this by explicitly checking for the presence of any constraints and returning an error if they are found, thus preventing the silent failure mode. The identified vulnerable functions, keyring.Add and client.Add, are the entry points for adding keys to the agent and are the precise locations where the lack of validation occurred.

Vulnerable functions

keyring.Add

ssh/agent/server.go

The `keyring.Add` function is responsible for adding keys to the in-memory keyring. The vulnerability lies in the fact that this function did not check for the presence of constraints on the keys being added. As a result, constraints like `ConfirmBeforeUse` were silently ignored, allowing the key to be used for signing operations without the required user confirmation. This could lead to unauthorized actions if an attacker can trick a user or a process into using such a key.

client.Add

ssh/agent/client.go

The `client.Add` function in the SSH agent client is used to request the addition of a new key to the agent. The vulnerability in this function is that it did not validate the key's constraints before sending the add request to the agent. This allowed a client to add a key with constraints that the agent's keyring did not support, such as `ConfirmBeforeUse`. The agent would then silently ignore these constraints, leading to the same security issue as with `keyring.Add`.

Vulnerability Intelligence
Miggo AI

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WAF Rule

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Reasoning

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