OpenHuman Shell Tool Allowlist Bypass via Env-Prefix / find -execdir (CVE-2026-55743)

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.

建議回應

參考資料

1. 01

   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)

   欄位: content運算子: regex
2. 02

   find invoked with -execdir/-okdir - the flags is_args_safe() failed to block, executing an arbitrary command per matched file

   欄位: content運算子: regex
3. 03

   explicit CVE framing combined with the bypass mechanism keywords

   欄位: content運算子: regex

攻擊範例（規則會觸發）

1. GIT_PAGER=/tmp/payload.sh git log

2. LD_PRELOAD=/tmp/x.so git status

3. PYTHONSTARTUP=/tmp/x.py python3 -V

4. GIT_EXTERNAL_DIFF=/tmp/evil.sh git diff HEAD~1

5. find . -name '*.txt' -execdir /tmp/run.sh {} ;

以上為真實攻擊 payload 的脫敏版本，與規則一同版本化，作為 regression test——確保未來的修訂不會悄悄漏掉它們。

正常樣本（規則不會觸發）

1. Benign env var TZ does not spawn a subprocess - explicitly accepted by the patch

   TZ=UTC git log

2. Common benign inline env var assignment with no executable-path payload

   NODE_ENV=production npm test

3. Standard find -exec usage (already covered by allowlist), no -execdir/-okdir

   find . -name '*.log' -exec rm {} ;

4. Mitigation advisory text - no env assignment to an executable path preceding an allowlisted command

   Upgrade OpenHuman past 0.54.0 to fix the GIT_PAGER allowlist issue described in CVE-2026-55743.

已知誤報情境

• ▸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.

title: "OpenHuman Shell Tool Allowlist Bypass via Env-Prefix / find -execdir (CVE-2026-55743)"
id: ATR-2026-01959
rule_version: 1
status: draft
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 - Excessive Agency"
  owasp_agentic:
    - "ASI06:2026 - Tool Misuse"
  mitre_atlas:
    - "AML.T0049 - Exploit Public-Facing Application"
  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)\b(?: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|c,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)
    - 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
wild_fp_rate: 0
test_cases:
  true_positives:
    - input: "GIT_PAGER=/tmp/payload.sh git log"
      expected: triggered
      description: "Exact CVE PoC: GIT_PAGER prefix points git's pager at attacker payload, git log is allowlisted"
    - input: "LD_PRELOAD=/tmp/x.so git status"
      expected: triggered
      description: "LD_PRELOAD injects a shared object into the allowlisted git process"
    - input: "PYTHONSTARTUP=/tmp/x.py python3 -V"
      expected: triggered
      description: "PYTHONSTARTUP runs attacker code before the allowlisted python3 -V"
    - input: "GIT_EXTERNAL_DIFF=/tmp/evil.sh git diff HEAD~1"
      expected: triggered
      description: "GIT_EXTERNAL_DIFF hook executes the payload during an allowlisted git diff"
    - input: "find . -name '*.txt' -execdir /tmp/run.sh {} ;"
      expected: triggered
      description: "find -execdir bypasses the -exec/-ok allowlist check, running an arbitrary command per file"
  true_negatives:
    - input: "TZ=UTC git log"
      expected: not_triggered
      description: "Benign env var TZ does not spawn a subprocess - explicitly accepted by the patch"
    - input: "NODE_ENV=production npm test"
      expected: not_triggered
      description: "Common benign inline env var assignment with no executable-path payload"
    - input: "find . -name '*.log' -exec rm {} ;"
      expected: not_triggered
      description: "Standard find -exec usage (already covered by allowlist), no -execdir/-okdir"
    - input: "Upgrade OpenHuman past 0.54.0 to fix the GIT_PAGER allowlist issue described in CVE-2026-55743."
      expected: not_triggered
      description: "Mitigation advisory text - no env assignment to an executable path preceding an allowlisted command"