Fix slasher OOM

[michaelsproul]

Issue Addressed

Fix a vulnerability in the slasher whereby it would OOM upon processing an invalid attestation with an artificially high validator_index. This fix has already been made available to affected users on the slasher-fix branch.

Proposed Changes

• Prevent attestations from being passed to the slasher prior to signature verification. This was unnecessary, as they would later be passed on successful validation as well.
• Add a defensive cap on the maximum validator index processable by the slasher. The cap is high enough that it shouldn't be reached for several years, and will quickly result in warning logs if forgotten.
• Add a regression test that confirms that the issue is fixed.

[jimmygchen]

nit: This loop is in acending validator_index right? would we want to break here if it happens?

[michaelsproul]

Good catch! Yeah it's a BTreeMap so a break makes sense

[michaelsproul]

Fixed in:

• e32a0c5

[jimmygchen]

Looks good and nice test!
Just a minor question on continue.

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-04-20 00:33 UTC · Rule: default
• ✅ Checks passed · on draft merge queue: embarking unstable (b561b59) and [#9106 + #9141] together #9146
• ✅ Merged — 2026-04-20 00:59 UTC · at e32a0c5cc912a19c83d2a4b34205fc6fd4b42c19 · squash

This pull request spent 26 minutes 38 seconds in the queue, including 26 minutes 19 seconds running CI.

Required conditions to merge

• #approved-reviews-by >= 1 [🛡 GitHub branch protection]
  • Fix total_effective_balance=0 in PreEpochCache #9106
  • Fix slasher OOM #9141
• #changes-requested-reviews-by = 0 [🛡 GitHub branch protection]
  • Fix total_effective_balance=0 in PreEpochCache #9106
  • Fix slasher OOM #9141
• check-success=local-testnet-success
• check-success=test-suite-success