Implement weak subjectivity safety checks #7347

eserilev · 2025-04-22T19:49:25Z

Issue Addressed

Closes #7273

Proposed Changes

ethereum/consensus-specs#4179

eserilev · 2025-04-22T19:51:33Z

hey @dapplion when you have a chance, could you take a look at what I have so far?

The general flow is

user sets the weak subjectivity period checkpoint via the existing wss-checkpoint flag
on startup, we make the weak subjectivity calculation, using the user provided ws checkpoint, the head snapshot and the most recent finalized checkpoint

If the user doesn't set a weak subjectivity checkpoint, what are we supposed to do here?

beacon_node/store/src/hot_cold_store.rs

dapplion · 2025-04-23T14:16:53Z

beacon_node/beacon_chain/src/builder.rs

+            let Ok(finalized_block) = fork_choice.get_finalized_block() else {
+                panic!("TODO(ws)")
+            };
+            if !store.is_within_weak_subjectivity_period(


Just use the head_snapshot.beacon_state to compute the weak subjectivity period. You don't need to fetch the head state's finalize state. For WS sync, the head state = the weak subjectivity checkpoint state. You don't need to fetch any more data:

compute ws_period from head state

get current epoch from clock

check current_epoch <= head_state.epoch + ws_period

No need to involve the store here

dapplion · 2025-04-23T14:22:22Z

consensus/types/src/beacon_state.rs

+            .safe_div(balance_churn_limit.safe_mul(200)?)?;
+        let weak_subjectivity_period = spec
+            .min_validator_withdrawability_delay
+            .safe_mul(epochs_for_validator_set_churn)?;


Where is this formula from? You should implement

https://github.com/ethereum/consensus-specs/blob/1937aff86b41b5171a9bc3972515986f1bbbf303/specs/phase0/weak-subjectivity.md?plain=1#L82

I'm using the updated forumla for electra

https://github.com/ethereum/consensus-specs/blob/dev/specs/electra/weak-subjectivity.md#modified-compute_weak_subjectivity_period

I think the calc is simpler now that top ups are part of activation churn

Ah right, please link it

Ah but we probably need to support the pre-electra calculation as well

dapplion · 2025-04-23T14:24:06Z

If the user doesn't set a weak subjectivity checkpoint, what are we supposed to do here?

We should assert that the initial state is within the weak subjectivity period on any type of start.

We should also offer a flag such that

If flag set and starting from outside weak subjectivity period: big warn log, continue start
If flag not set and starting from outside weak subjectivity period: error, abort start

dapplion · 2025-04-24T16:15:08Z

beacon_node/beacon_chain/src/builder.rs

+            }
+            return Err(
+                "The current head state is outside the weak subjectivity period. It is highly recommended to purge your db and \
+                checkpoint sync. Alternatively you can accept the risks and ignore this error with the --ignore-ws-check flag.".to_string()


We should either summarize "the risks" or link to some resource of our own. Otherwise it's quite opaque to the users.

i've summarized the risks and linked to a blog post by vitalik

eserilev · 2025-04-24T19:24:39Z

Thanks for all the help Lion. I've made changes based on your feedback and added additional test coverage

dapplion

Looks great now!

mergify · 2025-10-14T18:23:02Z

This pull request has merge conflicts. Could you please resolve them @eserilev? 🙏

consensus/types/src/state/beacon_state.rs

consensus/types/src/beacon_state.rs

mergify · 2025-12-02T16:33:57Z

Some required checks have failed. Could you please take a look @eserilev? 🙏

michaelsproul · 2025-12-03T01:19:11Z

There are some tests failures. Maybe we could use a small non-zero constant pre-Electra to smooth over this issue, or we could update these tests to only run post-Electra.

eserilev · 2025-12-03T01:48:53Z

Yeah I'm going to fix theses tests to run post Electra

…eserilev/lighthouse into weak-subjectivity-startup-check

eserilev · 2025-12-03T14:15:37Z

InvalidPayloadRig wasnt using the fork_from_env stuff when constructing spec so we weren't actually running related tests against RECENT_FORKS in some cases.

revert_minority_fork_on_resume was an annoying test to try to get right when setting the WS calculation to 0 pre-electra. Setting the calculation to a min of 5 fixes the test.

basic sim and fallback sim were also failing and I havent had a chance to look at why. I've ramped up the pre electra ws calc to 256 to fix this (5 was too small of a number apparently).

mergify · 2026-01-14T19:19:27Z

Some required checks have failed. Could you please take a look @eserilev? 🙏

…ak-subjectivity-startup-check

Add initial weak subjectivity check

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eserilev added electra Required for the Electra/Prague fork enhancement New feature or request work-in-progress PR is a work-in-progress labels Apr 22, 2025

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Add ignore-ws-check flag and changes based on feedback

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Merge branch 'unstable' into weak-subjectivity-startup-check

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eserilev added 2 commits December 2, 2025 13:00

Remove pre-electra calc

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Merge branch 'unstable' into weak-subjectivity-startup-check

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Use test spec in InvalidPayloadRig

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Merge branch 'weak-subjectivity-startup-check' of https://github.com/…

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…eserilev/lighthouse into weak-subjectivity-startup-check

eserilev added 3 commits December 3, 2025 11:15

WS pre-electra set to 5

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eserilev mentioned this pull request Jan 13, 2026

Flag to disable "unsafe" range sync #8657

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mergify bot added waiting-on-author The reviewer has suggested changes and awaits thier implementation. and removed ready-for-review The code is ready for review labels Jan 14, 2026

eserilev added 2 commits January 14, 2026 16:04

Merge branch 'unstable' of https://github.com/sigp/lighthouse into we…

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…ak-subjectivity-startup-check

Fix

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Implement weak subjectivity safety checks #7347

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Implement weak subjectivity safety checks #7347

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eserilev commented Apr 22, 2025

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