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https://issues.apache.org/jira/browse/GROOVY-12109?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18092025#comment-18092025
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ASF GitHub Bot commented on GROOVY-12109:
-----------------------------------------
paulk-asert opened a new pull request, #2634:
URL: https://github.com/apache/groovy/pull/2634
…eference cycle
> Harden Closure deserialization against owner/delegate reference cycle
> ---------------------------------------------------------------------
>
> Key: GROOVY-12109
> URL: https://issues.apache.org/jira/browse/GROOVY-12109
> Project: Groovy
> Issue Type: Improvement
> Reporter: Paul King
> Assignee: Paul King
> Priority: Major
>
> h2. Reject Closure owner/delegate reference cycles during deserialization
> h3. Cause (confirmed against groovy-5.0.6)
> A cyclic {{owner}}/{{delegate}} graph recurses forever through the MOP:
> {{CurriedClosure.call -> getOwner().call -> (owner is self) -> call -> ...}}.
> Or this similar pure-Groovy shape {{cl.delegate = cl; cl()}}. The graph
> serializes and deserializes cleanly; the blow-up is on first *invocation*.
> The only attacker-controlled way to build the cycle is a forged stream, so it
> is rejected there.
> h3. Options ruled out (break tested behaviour)
> || Option || Why it fails ||
> | Remove {{Serializable}} from {{Closure}} | Breaks all closure serialization
> + real users |
> | Make {{owner}}/{{delegate}}/{{thisObject}} {{transient}} | Fields come back
> {{null}}; {{Groovy11272.testSerialVersionUID_2/3}} serialize _without_
> {{dehydrate()}} and require the round-trip to stay callable |
> h3. Fix
> A {{readResolve}} hook on {{groovy.lang.Closure}} runs an iterative
> grey/black DFS over the raw {{owner}}/{{delegate}}/{{thisObject}} fields
> (Closure-valued links only) and throws {{InvalidObjectException}} on any
> cycle.
> Key design points:
> * *{{readResolve}}, not {{readObject}}* — a custom {{readObject}} interposes
> a core-loaded frame during field reads, shifting
> {{ObjectInputStream.latestUserDefinedLoader()}} off the script's
> {{GroovyClassLoader}} and breaking deserialization of captured generated
> types (caught by {{IntersectionClosureLiteralTest}}). {{readResolve}} runs
> after fields are read, so class resolution is untouched.
> * *Walk raw fields, not getters* — {{CurriedClosure.getDelegate()}} calls
> {{getOwner().getDelegate()}}, which would itself StackOverflow on the
> malicious graph.
> * *Grey/black DFS, not plain "visited"* — a curried closure's {{owner}} and
> {{delegate}} share the same wrapped clone (a diamond, not a cycle); naive
> detection false-positives on every curried closure.
> * {{MethodClosure}} already hard-blocks deserialization (CVE-2015-3253); its
> {{readResolve}} is only widened {{private}} -> {{protected}} to override the
> new hook (behaviour unchanged).
> h3. Validation
> || Graph || Detected? || Want ||
> | self-cycle ({{owner = this}}) — the PoC | (/) yes | yes |
> | A<->B two-closure cycle | (/) yes | yes |
> | legit simple closure | (/) no | no |
> | legit curried closure (shared clone) | (/) no | no |
> * New {{groovy.lang.ClosureSerializationCycleTest}} (4 tests): self-cycle
> rejected, A<->B cycle rejected, legit closure + legit curried closure
> round-trip.
> * Regression: previously-failing {{IntersectionClosureLiteralTest}} now
> passes; broad closure/serialization sweep all green.
> h3. Residual risk (by design)
> Does *not* prevent self-inflicted pure-Groovy recursion ({{cl.delegate = cl;
> cl()}}) — not a vulnerability, and scoped out deliberately. Hardening targets
> only the deserialization vector.
> h3. Change inventory
> || File || Change ||
> | {{groovy/lang/Closure.java}} | {{readResolve}} cycle check + private
> {{Marker}} sentinel; 3 new imports |
> | {{runtime/MethodClosure.java}} | {{readResolve}} {{private}} ->
> {{protected}} (behaviour unchanged) |
> | {{groovy/lang/ClosureSerializationCycleTest.groovy}} (NEW) | 4 tests |
> h3. Recommendation
> # Adopt the cycle-rejecting {{readResolve}} guard over a self-reference-only
> check (closes A<->B at no extra cost).
> # Decide the user-facing {{InvalidObjectException}} wording and whether a
> changelog note is warranted.
> # Run a full CI {{:test}} before merge — this path now runs on _every_
> closure deserialization.
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