claude-code/.claude/bash-permission-bug-analysis.md

Bash Permission Serialization Bug Analysis

Bug Description

When Claude Code saves bash permission rules to settings.local.json, malformed commands with unbalanced quotes can be stored. The validation that detects malformed patterns only runs when loading settings, not when saving them.

Reproduction Steps

1. Have Claude run a bash command containing quotes (e.g., arithmetic with quoted strings)
2. When permission is requested, click "Always Allow"
3. A malformed permission rule may be saved to settings.local.json
4. On next Claude Code startup, the settings fail to load with error:

   "Bash(250/0...
     └ 029 ")": Unmatched " in Bash pattern. Ensure all quotes are properly paired
   

Example Malformed Rule

{
  "permissions": {
    "allow": ["Bash(250/0.029 \")"]
  }
}

Root Cause Analysis

Code Flow

1. Permission Check (OE0 function):

   • Parses the bash command
   • Creates suggestions via UE0(command) or im5(prefix)
   • Returns suggestions to be shown in permission dialog

2. Suggestion Creation (UE0 function):

   function UE0(A){
     return[{
       type:"addRules",
       rules:[{toolName:M9.name, ruleContent:A}],
       behavior:"allow",
       destination:"localSettings"
     }]
   }
   

   • Takes command string directly as ruleContent
   • No validation that the command is well-formed

3. Saving Rules (_A1 function):

   function _A1({ruleValues:A, ruleBehavior:Q}, B){
     let G = A.map(s5);  // Serialize rules
     // ... save to settings
     nB(B, W);  // No validation before save
   }
   

4. Serialization (s5 function):

   function s5(A){
     if(!A.ruleContent) return A.toolName;
     let Q = HJ7(A.ruleContent);  // Escape parens/backslashes
     return `${A.toolName}(${Q})`
   }
   

   • Only escapes \, (, )
   • Does not validate quotes are balanced

5. Validation (only on load):

   let X = ['"', "'"];
   for(let W of X)
     if((J.match(new RegExp(W,"g"))||[]).length % 2 !== 0)
       return {
         valid: false,
         error: `Unmatched ${W} in Bash pattern`,
         suggestion: "Ensure all quotes are properly paired"
       };
   

The Gap

Validation exists but is only called when parsing settings, not when creating permission rules. This allows:

• Malformed commands from the model to be saved
• Commands with shell parsing errors to be saved
• Truncated or incorrectly reconstructed commands to be saved

Proposed Fix

Option 1: Validate Before Saving (Recommended)

Add validation in _A1 before saving:

function _A1({ruleValues: A, ruleBehavior: Q}, B) {
  if (A.length < 1) return true;

  // Validate each rule before saving
  for (const rule of A) {
    const serialized = s5(rule);
    const validation = validatePermissionRule(serialized);
    if (!validation.valid) {
      console.error(`Invalid permission rule: ${validation.error}`);
      return false;
    }
  }

  let G = A.map(s5);
  // ... rest of function
}

Option 2: Validate in UE0/im5

Add validation when creating suggestions:

function UE0(A) {
  // Validate command has balanced quotes
  const doubleQuotes = (A.match(/"/g) || []).length;
  const singleQuotes = (A.match(/'/g) || []).length;

  if (doubleQuotes % 2 !== 0 || singleQuotes % 2 !== 0) {
    // Don't create suggestion for malformed command
    return [];
  }

  return [{
    type: "addRules",
    rules: [{toolName: M9.name, ruleContent: A}],
    behavior: "allow",
    destination: "localSettings"
  }];
}

Option 3: Sanitize Command Before Creating Rule

If the command has unbalanced quotes, try to fix or reject it:

function sanitizeCommandForRule(command) {
  // Check for balanced quotes
  const dq = (command.match(/"/g) || []).length;
  const sq = (command.match(/'/g) || []).length;

  if (dq % 2 !== 0 || sq % 2 !== 0) {
    // Log warning and return null to skip this rule
    console.warn(`Skipping malformed command for permission rule: ${command}`);
    return null;
  }

  return command;
}

Additional Observations

1. The command parsing/reconstruction in VJ7 is complex and may have edge cases where commands are not properly reconstructed

2. The KE0 function uses quote markers (__DOUBLE_QUOTE__, __SINGLE_QUOTE__) for parsing which may not be fully restored in all cases

3. For piped commands, each segment is processed separately, increasing the chance of parsing errors

Recommended Fix Priority

1. Immediate: Add validation before saving in _A1 or $v functions
2. Short-term: Add better error handling when command parsing fails
3. Long-term: Review command reconstruction logic in VJ7 for edge cases

Related CHANGELOG Entries

• "Fixed permission rules incorrectly rejecting valid bash commands containing shell glob patterns"
• "Fixed Bash tool crashes caused by malformed shell syntax parsing"
• "Fixed security vulnerability in Bash tool permission checks"

These suggest this area of the code has had issues before.