Detect commands passed through simple launchers

Recognize fixed command positions without parsing launcher options. Only sanitize later arguments when the delegated command is one unchanged string literal.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: owen-mc

java/ql/lib/change-notes/2026-10-16-delegating-launchers.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* The `java/command-line-injection` query now detects command injection through simple invocations of delegating launchers such as `env`, `sudo`, and `timeout`.

java/ql/lib/semmle/code/java/JDK.qll

@@ -104,6 +104,14 @@ class StringPartialMatchMethod extends Method {
   }
 }
 
+/** The type `String[]`. */
+class ArrayOfStringType extends Array {
+  ArrayOfStringType() {
+    this.getDimension() = 1 and
+    this.getElementType() instanceof TypeString
+  }
+}
+
 /** The class `java.lang.StringBuffer`. */
 class TypeStringBuffer extends Class {
   TypeStringBuffer() { this.hasQualifiedName("java.lang", "StringBuffer") }
@@ -444,11 +452,7 @@ class MainMethod extends Method {
     this.getReturnType().hasName("void") and
     this.hasName("main") and
     this.getNumberOfParameters() = 1 and
-    exists(Array a |
-      a = this.getAParameter().getType() and
-      a.getDimension() = 1 and
-      a.getElementType() instanceof TypeString
-    )
+    this.getAParameter().getType() instanceof ArrayOfStringType
   }
 }
 

java/ql/lib/semmle/code/java/security/CommandArguments.qll

@@ -10,46 +10,145 @@ import semmle.code.java.Collections
 
 /**
  * Holds if `ex` is used safely as an argument to a command;
- * i.e. it's not in the first position and it's not a shell command.
+ * i.e. it's not in a position that selects a command to execute.
  */
 predicate isSafeCommandArgument(Expr ex) {
-  exists(ArrayInit ai, int i |
-    ex = ai.getInit(i) and
-    i > 0 and
-    not isShell(ai.getInit(0))
+  exists(ArrayInit init, int index |
+    ex = init.getInit(index) and
+    index > 0 and
+    isNonDelegatingCommand(init.getInit(0))
   )
   or
-  exists(CommandArgumentList cal |
-    not cal.isShell() and
-    ex = cal.getASubsequentAdd().getArgument(0)
+  exists(CommandArgumentList list |
+    not list.isShell() and
+    not list.isDelegatingLauncher() and
+    ex = list.getASubsequentAdd().getArgument(0)
   )
   or
-  exists(CommandArgArrayImmutableFirst caa |
-    not caa.isShell() and
-    ex = caa.getAWrite(any(int i | i > 0))
+  exists(CommandArgArrayImmutableFirst array |
+    not array.isShell() and
+    not array.isDelegatingLauncher() and
+    ex = array.getAWrite(any(int index | index > 0))
+  )
+  or
+  forex(CommandArguments arguments, int index | ex = arguments.getArgument(index) |
+    index > 0 and arguments.hasSafeDelegatedArgument(index)
   )
 }
 
-/**
- * Holds if the given expression is the name of a shell command such as bash or python
- */
-private predicate isShell(Expr ex) {
-  exists(string cmd | cmd = ex.(StringLiteral).getValue() |
-    cmd.regexpMatch(".*(sh|javac?|python[23]?|osascript|cmd)(\\.exe)?$")
-  )
+private string commandName(Expr ex) {
+  result = ex.(StringLiteral).getValue()
   or
   exists(SsaDefinition ssa, SsaExplicitWrite def |
     ex = ssa.getARead() and
-    isShell(def.getDefiningExpr())
+    result = commandName(def.getDefiningExpr())
   |
     ssa.getAnUltimateDefinition() = def
     or
     ssa.(SsaCapturedDefinition).getAnUltimateCapturedDefinition() = def
   )
   or
-  isShell(ex.(Assignment).getRhs())
+  result = commandName(ex.(Assignment).getRhs())
   or
-  isShell(ex.(LocalVariableDeclExpr).getInit())
+  result = commandName(ex.(LocalVariableDeclExpr).getInit())
+}
+
+/**
+ * Holds if the given expression is the name of a shell command such as bash or python
+ */
+private predicate isShell(Expr ex) {
+  commandName(ex).regexpMatch(".*(sh|javac?|python[23]?|osascript|cmd)(\\.exe)?$")
+}
+
+/**
+ * Gets the fixed position of the command executed by a supported delegating launcher.
+ *
+ * Only simple invocation forms with a command at the expected position are recognized. Launcher
+ * options and environment assignments are intentionally not interpreted.
+ */
+private int delegatedCommandIndex(Expr ex) {
+  exists(string launcher |
+    launcher = commandName(ex).regexpCapture("(.*/)?([^/.]+)(\\.exe)?$", 2) and
+    (
+      launcher = ["env", "nice", "nohup", "setsid", "sudo", "xargs"] and result = 1
+      or
+      launcher = ["chroot", "stdbuf", "timeout"] and result = 2
+    )
+  )
+}
+
+private predicate isNonDelegatingCommand(Expr ex) {
+  exists(commandName(ex)) and
+  not isShell(ex) and
+  not exists(delegatedCommandIndex(ex))
+}
+
+/** Holds if `init` initializes an array passed directly to a call. */
+private predicate isInlineArgumentArray(ArrayInit init) {
+  exists(ArrayCreationExpr array, Call call |
+    array.getInit() = init and
+    array = call.getAnArgument() and
+    not exists(MethodCall methodCall |
+      call = methodCall and
+      methodCall.getMethod().getDeclaringType().hasQualifiedName("java.util", "Arrays") and
+      methodCall.getMethod().hasName("copyOf")
+    )
+  )
+}
+
+private newtype TCommandArguments =
+  TLiteralArguments(ArrayInit init) { isInlineArgumentArray(init) } or
+  TListArguments(CommandArgumentList list) or
+  TMutableArguments(CommandArgArrayImmutableFirst array)
+
+/** An ordered sequence of command arguments. */
+private class CommandArguments extends TCommandArguments {
+  string toString() { result = this.getArgument(0).toString() }
+
+  /** Gets a possible value at the given index. */
+  Expr getArgument(int index) {
+    exists(ArrayInit init |
+      this = TLiteralArguments(init) and
+      result = init.getInit(index)
+    )
+    or
+    exists(CommandArgumentList list |
+      this = TListArguments(list) and
+      (
+        result = list.getArgument(index)
+        or
+        index = 3 and result = list.getAnArgumentAfterKnownPrefix().getArgument(0)
+      )
+    )
+    or
+    exists(CommandArgArrayImmutableFirst array |
+      this = TMutableArguments(array) and
+      result = array.getAnElement(index)
+    )
+  }
+
+  /** Gets the single string literal stored at the given index, if there is one. */
+  private StringLiteral getFixedLiteralArgument(int index) {
+    forex(Expr value | value = this.getArgument(index) | value = result)
+  }
+
+  predicate hasSafeDelegatedArgument(int index) {
+    exists(this.getArgument(index)) and
+    forex(Expr launcher | launcher = this.getArgument(0) |
+      forex(int commandIndex | commandIndex = delegatedCommandIndex(launcher) |
+        (
+          index < commandIndex
+          or
+          index > commandIndex and
+          exists(StringLiteral command |
+            command = this.getFixedLiteralArgument(commandIndex) and
+            not isShell(command) and
+            not exists(delegatedCommandIndex(command))
+          )
+        )
+      )
+    )
+  }
 }
 
 /**
@@ -101,6 +200,39 @@ private class CommandArgumentList extends SsaExplicitWrite {
     result.getQualifier() = this.getAUseBeforeFirstAdd()
   }
 
+  /** Gets a single-element addition at the given index. */
+  private MethodCall getAnAddAtIndex(int index) {
+    index = 0 and
+    result = this.getAFirstAdd() and
+    result.getMethod().hasName("add") and
+    result.getNumArgument() = 1
+    or
+    index > 0 and
+    index <= 2 and
+    exists(MethodCall previous |
+      previous = this.getAnAddAtIndex(index - 1) and
+      result = this.getAnAdd() and
+      result.getMethod().hasName("add") and
+      result.getNumArgument() = 1 and
+      adjacentUseUse(previous.getQualifier(), result.getQualifier())
+    )
+  }
+
+  /** Gets a single-element addition after the first three elements. */
+  MethodCall getAnArgumentAfterKnownPrefix() {
+    result = this.getAnAdd() and
+    result.getMethod().hasName("add") and
+    result.getNumArgument() = 1 and
+    exists(MethodCall previous |
+      previous = this.getAnAddAtIndex(2) or previous = this.getAnArgumentAfterKnownPrefix()
+    |
+      adjacentUseUse(previous.getQualifier(), result.getQualifier())
+    )
+  }
+
+  /** Gets the argument added at the given index. */
+  Expr getArgument(int index) { result = this.getAnAddAtIndex(index).getArgument(0) }
+
   /** Gets an addition to this list which is not the first element. */
   MethodCall getASubsequentAdd() {
     result = this.getAnAdd() and
@@ -109,15 +241,15 @@ private class CommandArgumentList extends SsaExplicitWrite {
 
   /** Holds if the first element of this list is a shell command. */
   predicate isShell() {
-    exists(MethodCall ma | ma = this.getAFirstAdd() and isShell(ma.getArgument(0)))
+    exists(MethodCall add | add = this.getAFirstAdd() and isShell(add.getArgument(0)))
   }
-}
 
-/**
- * The type `String[]`.
- */
-private class ArrayOfStringType extends Array {
-  ArrayOfStringType() { this.getElementType() instanceof TypeString }
+  /** Holds if the first element of this list is a delegating launcher. */
+  predicate isDelegatingLauncher() {
+    exists(MethodCall add | add = this.getAFirstAdd() |
+      exists(delegatedCommandIndex(add.getArgument(0)))
+    )
+  }
 }
 
 private predicate arrayVarWrite(ArrayAccess acc) { exists(Assignment a | a.getDest() = acc) }
@@ -153,7 +285,7 @@ private class CommandArgumentArray extends SsaExplicitWrite {
  */
 private class CommandArgArrayImmutableFirst extends CommandArgumentArray {
   CommandArgArrayImmutableFirst() {
-    (exists(this.getAWrite(0)) or exists(firstElementOf(this.getDefiningExpr()))) and
+    (exists(this.getAWrite(0)) or exists(arrayElementOf(this.getDefiningExpr(), 0))) and
     forall(VarRead use | exists(this.getAWrite(0, use)) | use = ssaGetAFirstUse(this))
   }
 
@@ -162,41 +294,56 @@ private class CommandArgArrayImmutableFirst extends CommandArgumentArray {
     result = this.getAWrite(0)
     or
     not exists(this.getAWrite(0)) and
-    result = firstElementOf(this.getDefiningExpr())
+    result = arrayElementOf(this.getDefiningExpr(), 0)
   }
 
   /** Holds if the first element of this array is a shell command. */
   predicate isShell() { isShell(this.getFirstElement()) }
+
+  /** Holds if the first element of this array is a delegating launcher. */
+  predicate isDelegatingLauncher() { exists(delegatedCommandIndex(this.getFirstElement())) }
+
+  /** Gets a possible value for the element at the given index. */
+  Expr getAnElement(int index) {
+    index = 0 and result = this.getFirstElement()
+    or
+    index > 0 and
+    (
+      result = this.getAWrite(index)
+      or
+      result = arrayElementOf(this.getDefiningExpr(), index)
+    )
+  }
 }
 
-/** Gets the first element of an imutable array of strings */
-private Expr firstElementOf(Expr arr) {
+/** Gets an element of an immutable array of strings. */
+private Expr arrayElementOf(Expr arr, int index) {
   arr.getType() instanceof ArrayOfStringType and
   (
-    result = firstElementOf(arr.(Assignment).getRhs())
+    result = arrayElementOf(arr.(Assignment).getRhs(), index)
     or
-    result = firstElementOf(arr.(LocalVariableDeclExpr).getInit())
+    result = arrayElementOf(arr.(LocalVariableDeclExpr).getInit(), index)
     or
     exists(CommandArgArrayImmutableFirst caa | arr = caa.getARead() |
-      result = caa.getFirstElement()
+      result = caa.getAnElement(index)
     )
     or
     exists(MethodCall ma, Method m |
       arr = ma and
       ma.getMethod() = m and
       m.getDeclaringType().hasQualifiedName("java.util", "Arrays") and
       m.hasName("copyOf") and
-      result = firstElementOf(ma.getArgument(0))
+      result = arrayElementOf(ma.getArgument(0), index)
     )
     or
     exists(Field f |
       f.isStatic() and
       arr.(FieldRead).getField() = f and
-      result = firstElementOf(f.getInitializer())
+      result = arrayElementOf(f.getInitializer(), index)
     )
     or
-    result = arr.(ArrayInit).getInit(0)
+    result = arr.(ArrayInit).getInit(index)
     or
-    result = arr.(ArrayCreationExpr).getInit().getInit(0)
+    result = arr.(ArrayCreationExpr).getInit().getInit(index)
   )
 }