CVE-2026-106583: OpenSSH Command Injection Vulnerability

CVE-2026-106583 Overview

CVE-2026-106583 is an argument injection vulnerability in the OpenSSH client (ssh) in versions before 10.6. The flaw allows $ or \ characters to appear in a command-line username, leading to injection into downstream command processing. The weakness is categorized under CWE-99: Improper Control of Resource Identifiers.

Exploitation requires local access and user interaction with an attacker-influenced username value, which limits practical impact. The issue was addressed in OpenSSH 10.6 per the OpenSSH Release Notes 10.6.

Critical Impact
An attacker who controls the username argument passed to ssh can inject shell metacharacters that are later interpreted by expansion or command-processing routines, potentially altering intended behavior.

Affected Products

OpenSSH ssh client versions prior to 10.6
Systems and scripts that pass untrusted input as the SSH username on the command line
Automation tooling that constructs ssh user@host invocations from external data

Discovery Timeline

2026-10-07 - CVE-2026-106583 published to the National Vulnerability Database (NVD)
2026-10-07 - Last updated in the NVD database

Technical Details for CVE-2026-106583

Vulnerability Analysis

The vulnerability resides in how the OpenSSH client parses and forwards a username supplied on the command line. When a username contains $ or \, the characters are not properly sanitized before being handed to subsequent processing paths. An attacker who can influence the username string, through a wrapper script, a configuration file, or a Git submodule URL, can inject additional directives.

The impact is scoped to local, low-complexity-bypassed exploitation requiring an existing low-privileged context. The outcome is limited integrity impact; confidentiality and availability are not directly affected. The classification under [CWE-99] highlights improper control of a resource identifier passed between components.

Root Cause

The ssh client accepts arbitrary characters, including shell-significant metacharacters, in the username field. The username is subsequently expanded or forwarded to other command-processing contexts without escaping $ (variable expansion) or \ (escape sequences). Downstream components interpret these characters, producing behavior different from what the invoking user intended.

Attack Vector

Typical exploitation paths include tools that build SSH command lines from external input. Examples include version control helpers, build systems, or orchestration scripts that interpolate a user-controlled identifier into ssh user@host invocations. An attacker who supplies a crafted username such as foo$(cmd) or foo\x can cause unintended expansion when the resulting command is processed by a shell or configuration parser further down the chain.

The vulnerability requires local access and user interaction with the crafted input. Remote network exploitation against a vulnerable client is not supported by the attack vector described in the advisory.

See the OpenSSH Release Notes 10.6 for upstream technical details.

Detection Methods for CVE-2026-106583

Indicators of Compromise

Shell history or process-audit records showing ssh invocations where the username argument contains $, \, backticks, or parentheses.
Unexpected child processes spawned from ssh or wrapper scripts that construct SSH command lines.
Automation logs where usernames read from external sources include shell metacharacters.

Detection Strategies

Audit scripts, CI/CD jobs, and Git tooling that build ssh command lines from untrusted input, and flag any that do not quote or validate the username.
Inventory installed OpenSSH client versions across the fleet and identify hosts running versions older than 10.6.
Use static analysis on shell scripts to detect unquoted interpolation of user-supplied values into ssh invocations.

Monitoring Recommendations

Enable Linux auditd rules for execve calls to /usr/bin/ssh and alert on argument values containing $ or \ in the username position.
Forward process-execution telemetry to a central SIEM or data lake and build a query that returns ssh processes with suspicious username arguments.
Monitor developer workstations and build agents, which are the most likely hosts to execute ssh with attacker-influenced identifiers.

How to Mitigate CVE-2026-106583

Immediate Actions Required

Upgrade the OpenSSH client to version 10.6 or later on all systems where ssh is invoked with externally sourced arguments.
Review automation that interpolates user-controlled strings into ssh command lines and add input validation that rejects shell metacharacters.
Prefer the explicit -l <username> form and validate the username against an allowlist such as ^[A-Za-z0-9._-]+$.

Patch Information

OpenSSH 10.6 contains the fix for CVE-2026-106583. Package maintainers for major Linux distributions typically backport such fixes; apply vendor updates once available. Reference the OpenSSH Release Notes 10.6 to confirm the fix is present.

Workarounds

Validate or sanitize any username value before passing it to ssh, rejecting $, \, backticks, quotes, and parentheses.
Where possible, specify the username in an SSH configuration file (~/.ssh/config) rather than on the command line.
Restrict execution of ssh wrappers that accept untrusted input, and ensure such wrappers quote arguments defensively.

bash

# Example: validate a username before invoking ssh
USER_INPUT="$1"
if ! printf '%s' "$USER_INPUT" | grep -Eq '^[A-Za-z0-9._-]+$'; then
  echo "Invalid username" >&2
  exit 1
fi
ssh -l "$USER_INPUT" host.example.com