title: OpenHuman Shell Tool Allowlist Bypass via Env-Prefix / find -execdir (CVE-2026-55743)
id: ATR-2026-01959
rule_version: 2
status: experimental
description: |
  Detects CVE-2026-55743 (CRITICAL): the shell tool command allowlist in OpenHuman desktop agent <= 0.54.0 (default Supervised SecurityPolicy) is bypassed because is_command_allowed() strips leading inline KEY=value environment-variable assignments (skip_env_assignments) before validation, and is_args_safe() blocks find -exec/-ok but not the functionally identical -execdir/-okdir. An attacker prefixes an allowlisted command with a dangerous env var (GIT_EXTERNAL_DIFF, GIT_SSH_COMMAND, GIT_PAGER, LD_PRELOAD, BASH_ENV, PYTHONSTARTUP) pointing at a payload, e.g. "GIT_PAGER=/tmp/payload.sh git log", so the allowlisted git binary executes the attacker-controlled subprocess. This rule keys on a dangerous env-var assignment (= path/command) immediately preceding an allowlisted binary, and on find with -execdir/-okdir.
author: ATR Community
date: 2026/06/29
schema_version: '0.1'
detection_tier: pattern
maturity: test
severity: critical
references:
  owasp_llm:
    - LLM06:2025
  owasp_agentic:
    - ASI05:2026
    - ASI02:2026
  mitre_atlas:
    - AML.T0050 - Command and Scripting Interpreter
    - AML.T0053 - AI Agent Tool Invocation
  mitre_attack:
    - T1190 - Exploit Public-Facing Application
  cve:
    - CVE-2026-55743
metadata_provenance:
  mitre_atlas: human-reviewed
  owasp_llm: human-reviewed
  owasp_agentic: human-reviewed
compliance:
  eu_ai_act:
    - article: '15'
      context: 'Article 15 (accuracy, robustness, cybersecurity) — runtime detection of this technique is a cybersecurity control for high-risk AI systems. Technique: OpenHuman Shell Tool Allowlist Bypass via Env-Prefix / find -execdir (CVE-2026-55743).'
      strength: primary
    - article: '9'
      context: 'Article 9 (risk management system) requires identified risks to be addressed by appropriate measures; this rule is a runtime risk-treatment control. Technique: OpenHuman Shell Tool Allowlist Bypass via Env-Prefix / find -execdir (CVE-2026-55743).'
      strength: secondary
  nist_ai_rmf:
    - subcategory: MP.5.1
      context: 'NIST AI RMF MAP 5.1 — likelihood and impact of the identified attack are characterised; this rule detects the adversarial input at runtime. Technique: OpenHuman Shell Tool Allowlist Bypass via Env-Prefix / find -execdir (CVE-2026-55743).'
      strength: primary
    - subcategory: MG.3.2
      context: 'NIST AI RMF MANAGE 3.2 — runtime monitoring/maintenance control that surfaces this attack class. Technique: OpenHuman Shell Tool Allowlist Bypass via Env-Prefix / find -execdir (CVE-2026-55743).'
      strength: secondary
  iso_42001:
    - clause: '8.1'
      context: 'ISO/IEC 42001 Clause 8.1 (operational planning and control) — detection of this payload is an operational control. Technique: OpenHuman Shell Tool Allowlist Bypass via Env-Prefix / find -execdir (CVE-2026-55743).'
      strength: primary
    - clause: '8.3'
      context: 'ISO/IEC 42001 Clause 8.3 (AI risk treatment) — this rule implements runtime detection as a treatment control. Technique: OpenHuman Shell Tool Allowlist Bypass via Env-Prefix / find -execdir (CVE-2026-55743).'
      strength: secondary
tags:
  category: tool-poisoning
  subcategory: shell-allowlist-env-prefix-bypass
  scan_target: both
  confidence: high
  source: cve-disclosure
  vendor_sources: openhuman-cve-2026-55743
agent_source:
  type: llm_io
  framework:
    - any
  provider:
    - any
detection:
  condition: any
  false_positives:
    - Benign inline env vars that do not spawn subprocesses (e.g. TZ=UTC git log, LANG=C ls, NODE_ENV=production npm test).
    - Legitimate use of find with -exec/-ok flags that are already covered by the allowlist, without -execdir/-okdir.
    - Documentation or advisory text that mentions GIT_PAGER or LD_PRELOAD without an assignment to an executable path preceding an allowlisted command.
  conditions:
    - field: content
      operator: regex
      value: (?i)(?:^|[\n;&|(`"\x27:,])[ \t]*(?:GIT_EXTERNAL_DIFF|GIT_SSH_COMMAND|GIT_PAGER|GIT_EDITOR|LD_PRELOAD|LD_AUDIT|LD_LIBRARY_PATH|BASH_ENV|ENV|PYTHONSTARTUP|PERL5OPT|PROMPT_COMMAND)=\S*\s*(?:/|\.{1,2}/|~/|\$\{?\w|[\w./-]+\.(?:sh|so|py|pl|bat))[^\n]{0,80}?\b(?:git|ls|cat|grep|find|python3?|node|npm|cp|mv|head|tail)\b
      description: |
        Dangerous environment-variable assignment to a path/command immediately preceding an allowlisted binary - the CVE-2026-55743 env-prefix allowlist bypass (e.g. GIT_PAGER=/tmp/payload.sh git log, LD_PRELOAD=/tmp/x.so git status). The assignment must sit at the START of a command (string start, newline, or after ; & | ( : , or an opening quote - the last three cover the command embedded in YAML/JSON tool arguments). That is what "prefix" means in skip_env_assignments: the function strips assignments that LEAD the command string, so `WRAPPER KEY=val allowlisted-cmd` is a different shape - the validated first token is then WRAPPER, which the Supervised policy allowlist rejects on its own. Without the anchor this condition also matched sudo/env-wrapped GTFOBins privilege-escalation one-liners, which are not this CVE. See evasion_tests for the shapes the anchor gives up.
    - field: content
      operator: regex
      value: (?i)\bfind\b[^\n]{0,200}?-(?:execdir|okdir)\b\s+\S
      description: |
        find invoked with -execdir/-okdir - the flags is_args_safe() failed to block, executing an arbitrary command per matched file
    - field: content
      operator: regex
      value: (?i)CVE-2026-55743[\s\S]{0,200}(?:allowlist|env(?:ironment)?[\s-]?(?:var|prefix)|execdir|skip_env|GIT_PAGER|LD_PRELOAD)
      description: explicit CVE framing combined with the bypass mechanism keywords
response:
  actions:
    - alert
    - block_input
  message_template: |
    [ATR-2026-01959] CRITICAL: OpenHuman shell allowlist bypass (CVE-2026-55743) - an inline dangerous env-var prefix or find -execdir/-okdir turns an allowlisted command into arbitrary OS command execution. Block and patch to > 0.54.0.
confidence: 85