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https://issues.apache.org/jira/browse/GROOVY-12109?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Paul King updated GROOVY-12109:
-------------------------------
Description:
h2. Reject Closure owner/delegate reference cycles during deserialization
{panel:title=Status|borderColor=#d97706|titleBGColor=#fef3c7}
*Proposed — pending team review.* Patch + tests implemented and green locally;
decision to ship (and exception wording) not yet ratified.
{panel}
h3. Summary
A hand-crafted serialized {{CurriedClosure}} whose {{owner}}/{{delegate}} point
at itself triggers a {{StackOverflowError}} when deserialized-and-invoked
(reported as a DoS; PoC uses _ysoserial_ + the JDK
{{AnnotationInvocationHandler}} gadget).
* *Is it a CVE?* (x) No — exploitation requires an app that deserializes
_untrusted_ data, which is itself the root vulnerability. Consistent with team
consensus.
* *Harden anyway?* (/) Yes — as defense-in-depth, _if_ legitimate closure
serialization is preserved. This change does that.
h3. Root 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
# Confirm "not a CVE" back to the reporter, with thanks; ship as
defense-in-depth, not a security release.
# 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.
> 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
> {panel:title=Status|borderColor=#d97706|titleBGColor=#fef3c7}
> *Proposed — pending team review.* Patch + tests implemented and green
> locally; decision to ship (and exception wording) not yet ratified.
> {panel}
> h3. Summary
> A hand-crafted serialized {{CurriedClosure}} whose {{owner}}/{{delegate}}
> point at itself triggers a {{StackOverflowError}} when
> deserialized-and-invoked (reported as a DoS; PoC uses _ysoserial_ + the JDK
> {{AnnotationInvocationHandler}} gadget).
> * *Is it a CVE?* (x) No — exploitation requires an app that deserializes
> _untrusted_ data, which is itself the root vulnerability. Consistent with
> team consensus.
> * *Harden anyway?* (/) Yes — as defense-in-depth, _if_ legitimate closure
> serialization is preserved. This change does that.
> h3. Root 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
> # Confirm "not a CVE" back to the reporter, with thanks; ship as
> defense-in-depth, not a security release.
> # 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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