|
| 1 | +/** |
| 2 | + * Provides class and predicates to track external data that |
| 3 | + * may represent malicious xpath query objects. |
| 4 | + * |
| 5 | + * This module is intended to be imported into a taint-tracking query |
| 6 | + * to extend `TaintKind` and `TaintSink`. |
| 7 | + */ |
| 8 | + |
| 9 | +import python |
| 10 | +import semmle.python.dataflow.TaintTracking |
| 11 | +import semmle.python.web.HttpRequest |
| 12 | + |
| 13 | +/** Models Xpath Injection related classes and functions */ |
| 14 | +module XpathInjection { |
| 15 | + /** Returns a class value which refers to `lxml.etree` */ |
| 16 | + Value etree() { result = Value::named("lxml.etree") } |
| 17 | + |
| 18 | + /** Returns a class value which refers to `lxml.etree` */ |
| 19 | + Value libxml2parseFile() { result = Value::named("libxml2.parseFile") } |
| 20 | + |
| 21 | + /** A generic taint sink that is vulnerable to Xpath injection. */ |
| 22 | + abstract class XpathInjectionSink extends TaintSink { } |
| 23 | + |
| 24 | + /** |
| 25 | + * A Sink representing an argument to the `etree.Xpath` call. |
| 26 | + * |
| 27 | + * from lxml import etree |
| 28 | + * root = etree.XML("<xmlContent>") |
| 29 | + * find_text = etree.XPath("`sink`") |
| 30 | + */ |
| 31 | + private class EtreeXpathArgument extends XpathInjectionSink { |
| 32 | + override string toString() { result = "lxml.etree.Xpath" } |
| 33 | + |
| 34 | + EtreeXpathArgument() { |
| 35 | + exists(CallNode call | call.getFunction().(AttrNode).getObject("XPath").pointsTo(etree()) | |
| 36 | + call.getArg(0) = this |
| 37 | + ) |
| 38 | + } |
| 39 | + |
| 40 | + override predicate sinks(TaintKind kind) { kind instanceof ExternalStringKind } |
| 41 | + } |
| 42 | + |
| 43 | + /** |
| 44 | + * A Sink representing an argument to the `etree.EtXpath` call. |
| 45 | + * |
| 46 | + * from lxml import etree |
| 47 | + * root = etree.XML("<xmlContent>") |
| 48 | + * find_text = etree.EtXPath("`sink`") |
| 49 | + */ |
| 50 | + private class EtreeETXpathArgument extends XpathInjectionSink { |
| 51 | + override string toString() { result = "lxml.etree.ETXpath" } |
| 52 | + |
| 53 | + EtreeETXpathArgument() { |
| 54 | + exists(CallNode call | call.getFunction().(AttrNode).getObject("ETXPath").pointsTo(etree()) | |
| 55 | + call.getArg(0) = this |
| 56 | + ) |
| 57 | + } |
| 58 | + |
| 59 | + override predicate sinks(TaintKind kind) { kind instanceof ExternalStringKind } |
| 60 | + } |
| 61 | + |
| 62 | + /** |
| 63 | + * A Sink representing an argument to the `xpath` call to a parsed xml document. |
| 64 | + * |
| 65 | + * from lxml import etree |
| 66 | + * from io import StringIO |
| 67 | + * f = StringIO('<foo><bar></bar></foo>') |
| 68 | + * tree = etree.parse(f) |
| 69 | + * r = tree.xpath('`sink`') |
| 70 | + */ |
| 71 | + private class ParseXpathArgument extends XpathInjectionSink { |
| 72 | + override string toString() { result = "lxml.etree.parse.xpath" } |
| 73 | + |
| 74 | + ParseXpathArgument() { |
| 75 | + exists( |
| 76 | + CallNode parseCall, CallNode xpathCall, ControlFlowNode obj, Variable var, AssignStmt assign |
| 77 | + | |
| 78 | + parseCall.getFunction().(AttrNode).getObject("parse").pointsTo(etree()) and |
| 79 | + assign.getValue().(Call).getAFlowNode() = parseCall and |
| 80 | + xpathCall.getFunction().(AttrNode).getObject("xpath") = obj and |
| 81 | + var.getAUse() = obj and |
| 82 | + assign.getATarget() = var.getAStore() and |
| 83 | + xpathCall.getArg(0) = this |
| 84 | + ) |
| 85 | + } |
| 86 | + |
| 87 | + override predicate sinks(TaintKind kind) { kind instanceof ExternalStringKind } |
| 88 | + } |
| 89 | + |
| 90 | + /** |
| 91 | + * A Sink representing an argument to the `xpathEval` call to a parsed libxml2 document. |
| 92 | + * |
| 93 | + * import libxml2 |
| 94 | + * tree = libxml2.parseFile("file.xml") |
| 95 | + * r = tree.xpathEval('`sink`') |
| 96 | + */ |
| 97 | + private class ParseFileXpathEvalArgument extends XpathInjectionSink { |
| 98 | + override string toString() { result = "libxml2.parseFile.xpathEval" } |
| 99 | + |
| 100 | + ParseFileXpathEvalArgument() { |
| 101 | + exists( |
| 102 | + CallNode parseCall, CallNode xpathCall, ControlFlowNode obj, Variable var, AssignStmt assign |
| 103 | + | |
| 104 | + parseCall.getFunction().(AttrNode).pointsTo(libxml2parseFile()) and |
| 105 | + assign.getValue().(Call).getAFlowNode() = parseCall and |
| 106 | + xpathCall.getFunction().(AttrNode).getObject("xpathEval") = obj and |
| 107 | + var.getAUse() = obj and |
| 108 | + assign.getATarget() = var.getAStore() and |
| 109 | + xpathCall.getArg(0) = this |
| 110 | + ) |
| 111 | + } |
| 112 | + |
| 113 | + override predicate sinks(TaintKind kind) { kind instanceof ExternalStringKind } |
| 114 | + } |
| 115 | +} |
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