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WIP: Go: CORS Bypass due to incorrect checks #16813
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Original file line number | Diff line number | Diff line change | ||||
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/** | ||||||
* @name Incorrect check on url | ||||||
* @description If a CORS policy is configured to accept an origin value obtained from the request data, it can lead to a policy bypass. | ||||||
* @kind path-problem | ||||||
* @problem.severity warning | ||||||
* @id go/cors-bypass | ||||||
* @tags security | ||||||
* experimental | ||||||
* external/cwe/cwe-942 | ||||||
* external/cwe/cwe-346 | ||||||
*/ | ||||||
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import go | ||||||
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bindingset[s] | ||||||
private predicate mayBeCors(string s) { s.toLowerCase().matches(["%origin%", "%cors%"]) } | ||||||
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/** | ||||||
* An argument to a Gorilla's OriginValidator Function taken as a source | ||||||
*/ | ||||||
class GorillaOriginFuncSource extends RemoteFlowSource::Range { | ||||||
GorillaOriginFuncSource() { | ||||||
exists(FuncDef f, DataFlow::CallNode c | | ||||||
// Find a func passed to `AllowedOriginValdiator` as a validator. | ||||||
// The string parameter supplied to the validator is a remote controlled string supplied in the origin header. | ||||||
// `gh.AllowedOriginValidator(func(origin string) bool{})` | ||||||
f.getParameter(0).getType() instanceof StringType and | ||||||
f.getNumParameter() = 1 and | ||||||
c.getTarget().hasQualifiedName("github.com/gorilla/handlers", "AllowedOriginValidator") and | ||||||
c.getArgument(0).asExpr() = f | ||||||
| | ||||||
DataFlow::localFlow(DataFlow::parameterNode(f.getParameter(0)), this) | ||||||
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Suggested change
There is no point saying data flows from |
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) | ||||||
} | ||||||
} | ||||||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. @owen-mc This does not seem to do what I need it to do. I tried quick-eval for just these lines. I can see they identify the source correct and the sinks correctly but the moment I run a dataflow query, it fails to see the flow. I can see there is no modification done to the source before the sink. So, i don't know what could be missing here. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Please can you give me an example of a path you'd expect to see? I've downloaded the db you provided in the bounty issue. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I get a different result from you - when I quick-eval this class on the current db for that repo I get 6 results - all the uses of There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Yes, I can see the There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Well, There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more.
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private class MaybeOrigin extends DataFlow::Node { | ||||||
MaybeOrigin() { | ||||||
exists(RemoteFlowSource r | | ||||||
// Any write where the variables name could suggest it has something to do with cors. | ||||||
exists(Write w | | ||||||
// Take `origin` in `origin := r.Header.Get(header)` as a source. | ||||||
mayBeCors(w.getLhs().getName()) and | ||||||
TaintTracking::localTaint(r, w.getRhs()) | ||||||
| | ||||||
this = r //or this.asInstruction() = w | ||||||
) | ||||||
or | ||||||
// Take the receiver, call or call arguments as source when any of their names match `maybeCors` | ||||||
exists(DataFlow::CallNode c, DataFlow::ArgumentNode a | | ||||||
TaintTracking::localTaint(r, a) and | ||||||
a.argumentOf(c.asExpr(), _) and | ||||||
mayBeCors([a.getStringValue(), c.getTarget().getName()]) | ||||||
| | ||||||
// When argument or receiver is `maybeCors` take them as origin source. | ||||||
// When the call name is `maybeCors` take the result as origin source | ||||||
// (this = c.getResult(_) or this = a) | ||||||
this = r | ||||||
) | ||||||
) | ||||||
} | ||||||
} | ||||||
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private module UrlFlow implements DataFlow::ConfigSig { | ||||||
Check warning Code scanning / CodeQL Data flow configuration module naming Warning
Modules implementing a data flow configuration should end in Config.
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predicate isSource(DataFlow::Node node) { | ||||||
node instanceof MaybeOrigin or node instanceof GorillaOriginFuncSource | ||||||
} | ||||||
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predicate isSink(DataFlow::Node node) { | ||||||
exists(DataFlow::CallNode mc, DataFlow::ArgumentNode a | | ||||||
// Get a call to `strings.HasSuffix(origin, allowedDomain)` | ||||||
mc.getTarget().hasQualifiedName("strings", "HasSuffix") and | ||||||
a = mc.getArgument(1) and | ||||||
// should not match ".domain.com" | ||||||
not ( | ||||||
a.asExpr().(StringLit).getExactValue().matches(".%") | ||||||
or | ||||||
exists(AddExpr w | w.getLeftOperand().getStringValue().matches(".%") | | ||||||
DataFlow::localFlow(DataFlow::exprNode(w), a) | ||||||
) | ||||||
) | ||||||
| | ||||||
mc.getArgument(0) = node | ||||||
) | ||||||
} | ||||||
} | ||||||
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private module Flow = TaintTracking::Global<UrlFlow>; | ||||||
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private import Flow::PathGraph | ||||||
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from Flow::PathNode source, Flow::PathNode sink | ||||||
where Flow::flowPath(source, sink) | ||||||
select sink.getNode(), source, sink, | ||||||
"This can lead to a Cross Origin Resource Sharing(CORS) policy bypass" |
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I don't think you actually want this to extend
RemoteFlowSource::Range
. Since this is a.ql
file, it can't be imported by any other files, so the only effects are within this file. Looking at the uses ofRemoteFlowSource
in this file, the only effect is thatMaybeOrigin
can include nodes fromGorillaOriginFuncSource
. But asMaybeOrigin
is only used innode instanceof MaybeOrigin or node instanceof GorillaOriginFuncSource
, this makes no difference.